Abstract: In order to find out the relationship between proteases and senescence, modified sodium dodecyl sulfate (SDS)-gelatin-polyacrylamide gel electrophoresis was exploited to analyze proteases activities of tomato (Lycopersicum esculentum Mill. cv. 918) fruit. Three proteases, named as SP-1, SP-2 and SP-3, respectively, were detected in red-ripe tomato fruit. All activities of these three proteases were changed during ripening and senescence. Followed by ethylene treatment, the activity of SP-2 was enhanced and the activities of SP-1 and SP-3 were showed up earlier. The opposite effects were observed by 1-methylcycloprop treatment. These results suggested that all SP-1, SP-2 and SP-3, regulated either by nature ripening or ethylene treatment, were senescence related proteases. The study provides reference for the relationship between proteases and senescence.