We used a DNA microarray to compare the gene expression profiles in liver among three groups of mice fed a diet containing 5% royal jelly (RJ), a diet containing 5% RJ stored at 40 degrees C for 7 d (40-7d RJ) or a control diet which provides the same total energy as RJ. Expression of 267 genes was increased or decreased by 1.8-fold or more in animals given the RJ diet for 14 d as compared with control diet, though serum total cholesterol, triglyceride, phospholipid, glucose, insulin and leptin levels were unaffected. Many genes involved in cell growth, signal transduction, energy metabolism and transcription regulation were responsive to the RJ diet. Among the 267 genes whose expression was altered by RJ, 60% showed no change or a reduced change in response to 40-7d RJ diet. The 40-7d RJ diet contained little 57-kDa protein, identified as a possible freshness marker of RJ. Furthermore, the RJ diet did not influence the gene expression of cytochrome P450 enzymes and detoxifying enzymes, whereas the 40-7d RJ diet increased the gene expression of glutathione S-transferase and glutathione peroxidase. Indeed, the RJ diet decreased the gene expression of cytochrome P450 4A14 (CYP4A14), which catalyzes peroxidation of endogenous lipids that is associated with nonalcoholic steatohepatitis and alcoholic liver disease, while the 40-7d RJ diet was not effective to decrease the gene expression of CYP4A14. The results indicate that the efficacy of RJ decreased and the toxicity of RJ increased during storage at high temperature. We suggest that application of DNA microarray technology to the biochemical evaluation of food safety may be effective for rapid and precise quality control.