A total of 125 fungal isolates belonging to 47 species of Aspergillus, Penicillium, Alternaria, Fusarium and Trichoderma were screened for phytase-producing ability. Aspergillus niger was the most active in terms of phytase production, and the isolates produced extracellular phytase. Aspergillus niger isolate AUMC 134 showed the highest phytase production, followed by isolates AUMC 19A, AUMC 48A and AUMC 8A. The optimum environment for phytase production of Aspergillus niger was pH at 5.0-5.5, temperature of 45-55°C and substrate concentration of 0.8-0.16 mM. The hydrolytic action of the phytases indicated sequential hydrolysis of phosphate esters of phytic acid. The tested fungal phytases exhibited relatively high thermal stability.