Chlorophyllase from Ailanthus altissima leaves has been purified 63-fold by a combination of heat treatment, ultracentrifugation, gel filtration, and chromatography on diethylaminoethyl cellulose. While the enzyme is inhibited to some degree by Triton X-100, a modification of the assay procedure of Klein and Vishniac has been shown to be far superior to the use of aqueous acetone systems. The enzyme was found to have a pH optimum on pheophytin a of 4.5. Chlorophylls a and b, pheophytins a and b, and pyropheophytin a were hydrolyzed by the enzyme while protochlorophyll a and 4-vinyl protochlorophyll a were not hydrolyzed but were competitive inhibitors. p-Nitrophenyl acetate was not hydrolyzed. The enzyme does not appear to contain an essential sulfhydryl group since sodium tetrathionate and p-chloromercuribenzoate did not affect its activity.