Abstract： Objective To investigate the role of caspase 3 in HMME-induced apoptosis in hypertrophic scar fibroblasts (HSFs).Methods Fibroblasts were obtained from 10 patients with untreated hypertrophic scar,and subjected to a primary culture.After 4 to 6 passages of culture,the HSFs were divided into 3 groups to remain untreated (control group),be treated with HMME followed by photodynamic therapy (HMME-PDT group),or the combination of HMME and Z-DEVD-FMK followed by photodynamic therapy (caspase 3 inhibitor group).At 12 hours after the therapy,HSFs were collected and immunofluorescence microscopy was used to observe the fluorescence intensity of caspase 3 after staining with fluorescein isocyanate (FITC) and popodium iodide (PI),flow cytometry was performed to determine the percentage of caspase 3-positive HSFs and apoptosis rate in HSFs after single staining with FITC and PI respectively.Results The fluorescence intensity of caspase 3 was weak in the control group and caspase 3 inhibitor group,but was strong in the HMME-PDT group.An increased percentage of caspase 3-positive HSFs was noted in the HMMEPDT group compared with the control group and caspase 3 inhibitor group (30.86％ ± 1.21％ vs.3.12％ ±0.28％ and 2.46％ ± 0.18％,t =19.92,21.76,both P ＜ 0.05).The apoptosis rate in HSFs was significantly higher in the HMME-PDT group and caspase 3 inhibitor group than in the control group(30.54％ ± 3.78％ and 10.46％ ± 2.15％ vs.2.45％ ± 0.22％,t =35.90,27.97,both P＜ 0.05),and higher in the HMME-PDT group than in the caspase 3 inhibitor group.Conclusions The apoptosis in HSFs induced by HMME-PDT is closely related to the activation of caspase 3,while caspase 3 seems to be dispensable for the apoptosis.