Phytase gene phyAI of A. ficuum AS3.324 was transformed into tobacco NC89, resulting in transgenic tobacco and phytase was expressed nonspecifically in tissue of tobacco. The amount of phytase protein expressed accounted for 17.6% of the total soluble protein of tobacco leaves (growing for 8 weeks). The transgenic phytase in tobacco was compared with A. ficuum AS3.324 and was found to have the same specific activity, pH, temperature adaptability and substrate specificity. The differences between the two were as follows: theoretical molecular weight of phytase coded byphyAI was 49.2 kDa, apparent molecular weights of A. ficuum AS3.324 and transgenic tobacco phytase were 68.5 and 76.0 kDa, respectively. Thermal stability of transgenic tobacco phytase was higher than A. ficuum AS3.324 phytase. After 80 degreesC 15 min heat treatment, the residual enzyme activity of the transgenic tobacco phytase was 4.6 times more than that of the A. ficuum AS3.324 phytase. (C) 2004 Elsevier Ltd. All rights reserved.