The tannase was prepared from Aspergillus niger, which was grown on a medium containing salts and an extract of myrobalans. The enzyme extracted with a mixture of toluene and water and precipitated with alcohol yielded a preparation having 65% the activity of the original mycelium. The activity was measured on methyl gallate by titrating the gallic acid liberated. Since ordinary buffers interfere, strontium hydroxide-gallic acid mixtures were used to control the pH. The reaction velocity was considerably greater at pH 4.8-4.0 than at pH 3.0.