The present study aims to utilize natural tannins as substrate by the tannase produced by Trichoderma harzianum MTCC10841 for gallic acid production. Tannin degradation efficiency of tannase was investigated using different tannin rich agro-residues as substrates. Amla fruit, tamarind seed, jamun leaves, mulberry leaves and keekar leaves proved to be better substrate than tannic acid. The result of enzymatic hydrolysis of these substrates was also observed by paper chromatography which showed the appearance of end product gallic acid. The optimum pH and temperature for the enzyme was 5.5 and 40oC respectively. The enzyme was found to be stable at 40oC for 2hr. Effect of various additives on tannase activity was also evaluated. Among the different metal salts tested, HgCl2 strongly inhibited the enzyme followed with ZnCl2 and MnCl2. The detergents (SDS, Tween-20, -60 and -80) did not affect enzyme activity while - mercaptoethanol and EDTA had inhibitory effect.