Abstract: The tomato fruits of harvested at green-mature were used as test materials.The tomato fruits were fumigated with 0.05 mmol·L^-1 methyl jasmonate（MeJA） after treated with 30 μmol·L^-1 Nω-hydroxy-nor-L-arginine（nor-NOHA,an inhibitor of arginase） under low pressure（-35 kPa）.The roles of arginase involved in MeJA-induced postharvest tomato fruit resistance against gray mold were studied, in order to explain the regulation mechanism of MeJA on postharvest disease resistance.The results showed that MeJA treatment largely promoted hydrogen peroxide content shortly after treatment, significantly induced activity of superoxide dismutase and peroxidase and significantly enhanced catalase activity during the later stages, and largely inhibited the enhancement of relative electrical conductivity and malondialdehyde.Meanwhile, MeJA treatment also induced the activities of phenylalanine ammonialyase,polyphenol oxidase,chitinase andβ-1,3-glucanase,and promoted the accumulation of total phenolic.However,these effects of MeJA treatment were partially counteracted in fruit treated with（nor-NOHA+MeJA）.Thus,the results suggested that arginase played important roles in MeJA-induced postharvest tomato fruit resistance against gray mold.