The detection of proteolytic enzyme in the juice of purple passion fruit (Passiflora edulis Sims) was carried out and the properties of the crude enzyme preparations were studied.1. It has been found that the optimum pH of two types of proteases in the juice of passion fruit was 2.3 and 5.7, using casein as a substrate. The former was designated as PFP-I (Passion fruit protease-I) and the latter, as PFP-II.2. The maximum activity of PFP-I against temperature was 40°C and that of PFP-II was 50°C. The thermal stability of the enzymes in the solution of pH 6 was shown to be completely inactivated at 70°C and 60°C for PFP-I and PFP-II, respectively. The activity of the enzymes was comparatively stable over a pH range of 2 to 4. Although in the sodium citrate solution at pH 6 PFP-II was inactivated after freezing for 3 days, it was suitable for both of the proteases to be stored at 5°C.3. The activity of PFP-I was inhibited by incubation with Fe++, Co++, Pb++, Ag+, Zn++ and Hg++, but activated by Mn++, Sn++ and Cd++. On the other hand, that of PFP-II was reduced by Co++, Pb++, Ag+, Ca++ and Cd++, but slightly enhanced by Fe++, Cu++, Mn++ and Zn++.4. The maximum activity of PFP-I was in the acid pH region and was unaffected by various inhibitors such as PCMB, PMSF and EDTA. Therefore, PFP-I was estimated to be an acid protease. PFP-II was considered to be a SH-protease since its activity decreased markedly by some SH-reagents alone, being increased by cysteine.5. As fruits matured, the amount of juice per fruit increased, while free organic acid in the juice decreased. The specific activity and the total activity of the proteases were increased remarkably.