Objective To investigate the effect of earthworm fibrinolysin on growth inhibition and induction of apoptosis in human gastric carcinoma cell line MGC803 and its mechanism.Methods Cell lines were treated with a series of concentrations of earthworm fibrinolysin.Cell proliferation was detected by MTT assay.DNA gel electrophoresis was performed and cell apoptosis rates were analyzed by flow cytometry.p53 protein expression was detected by immunocytochemistry.Results MTT assay showed that earthworm fibrinolysin inhibited the proliferation of human gastric carcinoma cell line MGC803.The growth inhibition was in a dose-dependent manner.After cells were treated with earthworm fibrinolysin(4 uku·ml-1)for 48 h,characristic DNA ladder on DNA gel electrophoresis appeared.Earthworm fibrinolysin of 2,4 and 8 uku·ml-1 at 48h induced the apoptosis of MGC803 cells and the apoptosis rates were(29.51±5.54)%,(61.63±7.12)% and (80.82±5.40)%,respectively.Compared with control group,the apoptosis rates were significantly increased(P<0.01).Earthworm fibrinolysin of 2 and 3 uku·ml-1 at 48 h decreased p53 protein expression.The light intensity was 1.299±0.07 and 1.203±0.06,respectively.Compared with control group,the light intensity was significantly decreased(P<0.01).Conclusion Earthworm fibrinolysin inhibits the growth of human gastric carcinoma cell line MGC803 in vitro,which may be explained by its inhibitory effect on p53 and induction of apoptosis.