We report on the screening of different enzymes such as arylamidases, lipases, proteinases, and glucosidases in plant extracts of the Cactaceae family, genus Opuntia, as well as on a newly purified plant proteases from O. ficus-indica fruit extracts. These proteinases showed the maximum activity at pH 5.2 and 55 degrees C and FTC-casein was the best of the screened substrates. Proteolytic activities were activated by anti-oxidant compounds and by some divalent cations. These proteinases were efficiently inhibited by cystein proteinase inhibitors and by 1,10-phenanthroline. The estimated M-r for the main proteolytic activity was about 23.2 kDa. The results on milk clotting characteristics suggest a potential use of the fruit cystein enzymes of this plant in dairy industries.