Deltamethrin (DEL) and thiacloprid (THIA) are two insecticides that are widely used in agriculture either separately or in combination. Studies on genotoxicity and cytotoxicity of TIA and the mixture of DEL and THIA insecticides have not been reported so far. Therefore, we investigated the cytotoxic and genotoxic effects of commercial formulations DEL and/or THIA in rat bone marrow cells, using mitotic index (MI), micronucleus (MN) and chromosome aberrations (CA) assay. In vivo cytokinesis-block micronucleus (CBMN) assay using cytochalasin-B in bone marrow cells was performed for the first time in this study. Rats were orally gavaged with a single dose of DEL (15 mg/kg), THIA (112.5 mg/kg) or DEL + THIA (15 + 112.5 mg/kg) for 24 h (acute treatments), or DEL (3 mg/kg/day), THIA (22.5 mg/kg/day) or DEL + THIA (3 + 22.5 mg/kg/day) for 30 days (subacute treatments). A corn oil vehicle control group and cyclophosphamide (50 mg/kg) positive control group were also included. All DEL and/or THIA treatments significantly decreased MI and binucleated (BN) cell numbers, and significantly increased CA, as compared to the vehicle control group. The results of CBMN assay indicated that the combination of DEL and THIA for both treatment times and the 30-day treatment with THIA alone caused a significant increase in micronucleus formation in BN cells. The present findings indicated the combined exposure of DEL and THIA showed genotoxic and cytotoxic effects more than those of individual exposure of DEL or THIA in rat bone marrow cells. © 2011 Wiley Periodicals, Inc. Environ Toxicol 28: 524–531, 2013.