The study was designed to 1) evaluate the cytotoxic potential effects of different concentrations of 50nm AuNRs on mouse splenocytes chromosomal aberrations; 2) to examine the effect of different concentrations of 50nm AuNRs on human lung cancer (A549), Hepatic cancer (HepG2), colorectal cancer (Caco-2) cell lines, and normal lung (CCD-19Lu) cell line as a control. Cytotoxicity was evaluated using MTT (3-(4,5-dimethizzol-zyl)-2,5- diphenyl tetrazolium bromide) assay; 3) cell cycle assay was conducted using flow cytometry. Results indicated that 50nm AuNRs induced chromosomal aberrations in cultured mouse splenocytes in a dose-dependent manner. All the examined doses of 50 nm AuNRs were cytotoxic to mice splenocytes, and it induced most the aberration types, structurally (including chromatid gaps, chromatid breaks, deletions, and fragments, and numerically which represented as diploidy when compared with negative control. While 6.25 µg/ml 50nm AuNRs were safe when applied to cultured splenocytes. Also, results showed that 50nm AuNRs induced profound cytotoxicity in cancer cells of human colon cancer (Caco-2) (IC50 = 73.36), and human liver cancer (HepG2) (IC50 = 67.72), human lung cancer cell line (A549) (IC50 = 33.97), respectively. Moreover, AuNRs has cytotoxic activity on normal lung (CCD-19Lu) (IC50 = 545.5). Flow cytometric analysis demonstrated that 50nm AuNRs have a cytotoxic effect on human carcinoma cells (HepG2, CaCo2, A549, and CDD-19Lu) cells through the increased G2/M phase cell cycle arrest. In conclusion, these data indicate that 50nmAuNRs have cytotoxic and genotoxic effects on mouse splenocytes and human normal and cancer cell lines at a concentration-dependent manner.