BACKGROUND:  Phytase is increasingly used as an ingredient in swine and poultry feeds to improve the bioavailability of phytate-bound phosphorus and reduce the supplement of elemental phosphorus in feeds.  Recently, a transgenic rise (TGR) with phytase appA gene from E. coli has been developed in Taiwan.  To assure the food safety of this TGR, we performed a sub-chronic whole-food feeding study with Wistar rats. RESULTS:  Weaned feeding male and female rats were divided into TGR and non-TGR (NTGR) groups (20 rats per group), and fed diets containing 76.8% rice flour of TGR and NTGR, respectively.  After 93 days feeding, although some hematological findings and blood chemistry values differed significantly between the TGR and NTGR groups, all values were still within the normal range for rats of this age and sex.  No adverse effects of TGR were observed in terms of animal behavior, weight gain, or feed utilization rate.  Necropsy at the end of the experiment indicated that neither pathological lesions nor histopathological abnormalities were present in organs such as liver, kidney, intestines and testes of rats in TGR and NTGR groups.  In addition, no significant differences (P > 0.05) were observed in relative organ weights, hemograms and blood indices of rats between the two groups. CONCLUSION:  These results demonstrated that in a 93-day feeding study with Wistar rats a diet containing 76.8% of TGR flour having a phytase activity of about 1500 U kg-1 body weight per day has no adverse effects.