An esterase from Lycoperdon pyriforme was characterized. The enzyme had a maximum activity at pH 8.0 and 40C with p-nitrophenyl acetate as a substrate. Km and Vmax values were calculated as 2.13mM and 0.65 U/mg protein, respectively. The enzyme activity was conserved more than 90% over a broad range of pH (3.09.0) at 4C after 24h of incubation. The activity increased 37 +/- 3.6% after 120min of incubation at 40C. Li+, Mg2+ and Ca2+ activated the enzyme 12 +/- 1.8, 16 +/- 2.5 and 15 +/- 2.5%, respectively. The esterase was inhibited in different ratios by some detergents such as Triton X-114, Triton X-100, Tween 20 (Sigma Chemical Co., St. Louis, MO) and sodium dodecylsulfate. It retained most of its activity in the presence of methanol and dimethylsulphoxide at the final concentration of 10% (v/v). pH and moderate thermal stability of L.pyriforme esterase and its activity in some organic solvents could make it useful for some industrial purposes such as detergent and paper industry. PRACTICAL APPLICATIONS Esterases play a major role in the degradation of natural materials and industrial pollutants, viz., cereal wastes, plastics and other toxic chemicals. They are also useful in the synthesis of optically pure compounds, perfumes and antioxidants. Because of these biocatalytic applications, it may be interesting to study novel esterases from different organisms. Therefore, it is important to study esterase activity of Lycoperdon pyriforme. In this way, a new esterase having potential applications can be found.