Zizyphi spinosi semen (Z. spinosi) has been used in traditional Chinese medicine for the treatment of rheumatoid arthritis and wounds. However, toxicity in high doses was often observed due to the presence of alkaloids. This study was conducted to investigate the potential genotoxicity of Z. spinosi in vitro and in vivo. This was examined by the Bacterial reverse mutation (Ames) test using Salmonella typhimurium TA98, TA100, TA1535, TA1537 and Escherichia coli WP2uvrA, Chromosomal aberration was investigated using Chinese hamster lung cells and the micronucleus test using mice. Z. Spinosi did not induce mutagenicity in the Ames test, and it did not produce chromosomal aberration in Chinese hamster lung cells with and without metabolic activation, nor in the micronucleated polychromatic erythrocytes in the bone marrow cells in mice. Based on these results, it is concluded that Z. spinosi does not have mutagenic potential under the conditions examined in each study.