To analyse the influence of genetically modified (GM) rice (Oryza sativa) containing the exogenous choline oxidase (codA) gene on physiological metabolism and genetic horizontal transformation in the fed rats, the animals were divided randomly into two groups. One group was fed with the feedstuff containing 30% of transgenic rice. The remaining (control) group was fed with the feedstuff containing 30% of non-transgenic rice. After 30 days, growth, physiological metabolism parameters such as growth hormone (GH), insulin, glucagon, 3,3′,5-triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH), and the genetic horizontal transformation were analysed. Results indicated that the weight of all rats from the two groups was similar (P>0.05). Also, there was no significant difference in the level of GH, insulin, glucagon, T4, T3 and TSH between the treated and untreated rats. The serum urea nitrogen (SUN), glucose, the glutamate–pyruvate transaminase (GTP), as well as the total cholesterol, of treated rats were almost identical to those of the control (P>0.05). Moreover, no target DNA sequence of rice endogenous sucrose phosphate synthase (SPS) gene or exogenous choline oxidase (codA) gene was detected in organs (liver, muscle, pancreas, etc.) except the stomach, gastrointestinal and rectum contents, and no genetic horizontal transformation was observed in rats fed with transgenic rice.