The present study was undertaken to investigate the protective effect of royal jelly (RJ) against toxicity induced by a synthetic pyrethroid insecticide, lambda-cyhalothrin (LCT), in Swiss albino mice. Animals were randomly divided into six groups of six animals each. The control group received distilled water alone, whereas mice in the treatment groups received RJ alone (100 or 250 mg/kg of body weight), LCT alone (668ppm), or RJ+LCT for 21 days. All mice (100%) survived until the end of experiment and were sacrificed at the end of 24 hours. Blood, bone marrow, and liver and kidney tissues were analyzed for aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), creatinine, malondialdehyde (MDA), and reduced glutathione (GSH) levels and micronucleus (MN) frequency, chromosomal aberrations (CAs), and pathological damages. Serum AST, ALT, BUN, and creatinine levels were elevated in mice treated with LCT alone compared with the other tested groups (P<.05). LCT-induced oxidative damage caused a significant decrease in GSH levels and a significant rise in MDA levels of liver and kidney tissues. LCT alone-treated mice presented higher frequencies (P<.05) of MNs, CAs, and abnormal metaphases compared with the controls; moreover, the mitotic index was lower than in controls (P<.05). Oral treatment with RJ significantly ameliorated the indices of hepatotoxicity, nephrotoxicity, lipid peroxidation, and genotoxicity induced by LCT. Both doses of RJ tested provided significant protection against LCT-induced toxicity, and its strongest effect was observed at the dose level of 250 mg/kg of body weight. In vivo results suggest that RJ is a potent antioxidant against LCT-induced toxicity, and its protective effect is dose dependent. © 2011 Mary Ann Liebert, Inc.