Objective: To investigate the effect of 5-aminolevulinic（ALA）-photodynamic therapy（PDT） on the expressions of MMP-9

MMP-13 and TIMP-1 of hypertrophic scar model in rabbit ears

and analyze the possible therapeutic mechanisms of ALA-PDT treatment to hypertrophic scars of rabbit ears. Methods: The experimental animals were randomly divided into normal control

negative control

high concentration of ALA-PDT

low concentration of ALA-PDT and PDT groups. The latter three groups received ALA-PDT treatment or PDT treatment once a week for 3 weeks. The specimens of the rabbits were collected respectively 1

2 and 3 months after treatment to be used for RT-PCR and Western-blot test. Results: 1

2 and 3 months after PDT treatment

the expressions of MMP-9 and MMP-13（including mRNA and protein） in hypertrophic scar tissues of three treatment groups were significantly higher than those of the negative control group（P<0.01）

and the expression of TIMP-1 mRNA and protein of three treatment groups were significantly lower than that of the negative control group（P<0.01）. There were also significant differences between high-concentration ALA-PDT treatment group and the low one（P<0.05）. Conclusion: ALA-PDT is effective in treating hypertrophic scars of rabbit ears

and its possible therapeutic mechanisms are that ALA-PDT treatment generates oxidation activation effect to activate the activity of MMPs and induces the photoaging of fibroblasts of hypertrophic scar tissues of rabbit ears to inhibit the activity of TIMPs

which causes the up-regulation of MMPs and the down-regulation of TIMPs. Because of this

the degradation of collagen and ECM is accelerated and the formation of scars is suppressed.