Abstract: Objective To explore the expression levels of matrix metalloproteinase-9 (MMP-9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) protein and the change of MMP-9/TIMP-1 ratio in wound exudates of patients with stages Ⅲ and Ⅳ pressure ulcers during wound healing. Methods From July 2017 to July 2018, 30 patients with stage Ⅲ pressure ulcers [30 wounds, 16 males and 14 females, aged (65±10) years] and 34 patients with stage Ⅳ pressure ulcers [50 wounds, 17 males and 17 females, aged (65±9) years] admitted to Hebei General Hospital who met the inclusion criteria were enrolled in this prospective cohort study. According to the principle of wound treatment and the characteristics and needs of wound in different periods, individualized intervention measures were formulated for patients and appropriate dressings were selected. At the time of admission and on 7, 14, 21, 28 days of treatment, the healing of pressure ulcer wounds was evaluated by Pressure Ulcer Healing Scale. Afterwards, the wound exudate was collected at each time point to detect the expression levels of MMP-9 and TIMP-1 protein by enzyme-linked immunosorbent assay, and the MMP-9/TIMP-1 ratio was calculated. Data were processed with analysis of variance for repeated measurements of single group and linear trend test. Results (1) There were significantly statistical differences in wound healing scores of patients with stages Ⅲ and Ⅳ pressure ulcers among the time of admission and on 7, 14, 21, 28 days of treatment within each stage (F=145.382, 153.234, P<0.01), and they all showed a gradually decreasing trend (F=170.466, 284.585, P<0.01). (2) At the time of admission and on 7, 14, 21, 28 days of treatment, the expression levels of MMP-9 protein in wound exudates of patients with stages Ⅲ and Ⅳ pressure ulcers were (171±104), (138±88), (110±70), (85±55), (62±41) ng/L and (193±107), (173±104), (139±83), (114±70), (89±56) ng/L, respectively. There were significantly statistical differences within each stage (F=58.007, 111.680, P<0.01), and they all showed a gradually decreasing trend (F=62.901, 134.628, P<0.01). At the time of admission and on 7, 14, 21, 28 days of treatment, the expression levels of TIMP-1 protein in wound exudates of patients with stages Ⅲ and Ⅳ pressure ulcers were (6.2±3.9), (5.6±3.4), (5.1±3.1), (4.4±2.5), (3.8±2.3) ng/L and (4.8±2.5), (4.7±2.6), (4.4±2.6), (4.6±2.7), (4.1±2.4) ng/L, respectively. There were significantly statistical differences within each stage (F=25.479, 7.778, P<0.01), and there was a gradually decreasing trend in stage Ⅲ (F=62.901, P<0.01) and a decreasing trend in stage Ⅳ (F=134.628, P<0.01). At the time of admission, the expression levels of MMP-9 and TIMP-1 in wound exudates of patients with stage Ⅲ pressure ulcers were similar to those of patients with stage Ⅳ pressure ulcers (t=-1.03, 1.47, P>0.05). (3) At the time of admission and on 7, 14, 21, 28 days of treatment, the MMP-9/TIMP-1 ratios in the wound exudates of patients with pressure ulcers of stages Ⅲ and Ⅳ were 30±13, 25±9, 22±9, 20±8, 17±6 and 43±19, 37±13, 32±10, 26±9, 22±9, respectively. There were significantly statistical differences within each stage (F=37.173, 97.191, P<0.01), and they all showed a gradually decreasing trend (F=54.183, 130.088, P<0.01). At the time of admission, the MMP-9/TIMP-1 ratio in wound exudates of patients with stage Ⅳ pressure ulcers was significantly higher than that of patients with stage Ⅲ pressure ulcers (t=-3.42, P<0.01). Conclusions During the wound healing process of patients with stages Ⅲ and Ⅳ pressure ulcers, the expression levels of MMP-9 and TIMP-1 protein and the MMP-9/TIMP-1 ratio in wound exudates show a decreasing trend. The stage of wound healing can be predicted according to the expression level of MMP-9 protein and the MMP-9/TIMP-1 ratio.