Abstract: Objective To observe the clinical effects of sequential treatments of pulsed dye laser (PDL) and ablative fractional carbon dioxide laser on early stage hypertrophic burn scars. Methods From January 2016 to December 2017, 221 patients with 228 hypertrophic scars in all parts of body within 6 months post healing, conforming to the study criteria and treated in our department, were included in this prospective study. They were first treated by PDL, repeated at an interval of one month until the vascularity score of scar fell below 2 points, and then treated by ablative fractional carbon dioxide laser, repeated at an interval of 3 months. Their start time and numbers of treatment and follow-up time were recorded. Before the first treatment (hereinafter referred to as before treatment) and at the last follow-up (hereinafter referred to as after treatment), the vascularity, thickness, and pliability of scars were scored by a self-made scar rating scale. The scores of patients with the observation time between 6 to18 months post healing were compared among scars of patients grouped by age, body site of scar, starting time of treatment and numbers of treatment. The laser speckle contrast imaging technique was used to measure the blood flow value of scars. The itching symptom of the scars was evaluated by the Verbal Rating Scale. The satisfaction to the final effects of the doctors and patients was investigated and scored separately by Likert scale after treatment. The therapeutic or adverse reactions were recorded during the treatment. Data were processed with paired t test, Mann-Whitney U test, Wilcoxon signed rank sum test, Kruskal-Wallis H test, and Spearman rank correlation analysis. Results (1) The patients were treated on (64±36) d post healing, by PDL for (2.5±1.3) times and by ablative fractional carbon dioxide laser for (2.2±1.2) times. The follow-up time was (331±189) d. (2) The vascularity, thickness, pliability scores and total scores of scars were (1.4±0.9), (2.0±0.8), (1.7±0.8), and (5.0±2.1) points respectively after treatment, which were significantly lower than those before treatment [(4.1±0.7), (3.1±0.8), (3.0±0.9), and (10.2±2.0) points respectively, t=43.332, 24.968, 28.063, 46.394, P<0.01]. (3) Among the 123 scars from 120 patients with observation time between 6 to 18 months post healing, there were no statistically significant differences in the vascularity, thickness, pliability scores and total scores of scars among patients with different ages after treatment (χ²=4.339, 1.826, 1.375, 2.879, P>0.05). There was only significant difference in the pliability scores of scars among different body sites (χ²=13.530, P<0.05). There were statistically significant differences in the vascularity, thickness, pliability scores and total scores of scars with different starting time of treatment (χ²=30.725, 25.233, 25.119, 35.798, P<0.01). There were significantly positive correlation between starting time of treatment and the vascularity, thickness, pliability scores and total scores of scars (r=0.492, 0.442, 0.446, 0.532, P<0.01). There were statistically significant differences in the vascularity, pliability scores and total scores of scars with different numbers of treatment (Z=4.883, 4.910, 5.049, P<0.05). There were significantly negative correlation between number of treatment and the vascularity, thickness, pliability scores and total scores of scars (r=-0.176, -0.131, -0.191, -0.201, P<0.05). (4) The blood flow values were determined in 18 scars of 18 patients. The results showed that the blood flow values of scars after treatment were significantly decreased compared with those before treatment (t=7.230, P<0.01). (5) The pruritus scores of scars of patients after treatment were significantly decreased compared with those before treatment (Z=12.818, P<0.01). (6) There were significant differences between the satisfaction scores of doctors and the scores of patients after treatment (t=12.130, P<0.01). (7) After PDL treatment, there were some edema and purpura reactions for all the patients, and 11 (5.0%) patients had blisters. After ablative fractional carbon dioxide laser treatment, 4 (1.8%) patients had blisters, 5 (2.3%) patients suffered inflammatory reaction and erosion, and 9 (4.1%) patients suffered pigmentation. Conclusions The scores of hypertrophic burn scars can be obviously improved by sequential treatments of PDL and ablative fractional carbon dioxide laser. The effects can be more obvious with the earlier starting time and more numbers of treatment. The laser treatments can also decrease the blood flow values and alleviate the pruritus of scars, with high satisfaction of both patients and doctors.