Sunset Yellow (SY) is an organic azo dye that is used extensively as a coloring agent in many industries, such as cosmetics, pharmaceuticals ,and foodstuffs. Many studies have conflicting results about the genotoxicity effect of SY. Thus, the purpose of this study was to provide additional data concerning SY genotoxicity in human lymphocytes by using chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs) assay. Four concentrations of Sunset Yellow (1, 5, 20 ,and 50 mg/ml) were used on human lymphocyte cultures. Positive and negative controls were mitomycin C and distilled water, respectively. Compared to the control, SY caused a significant increase in CAs and SCEs frequencies at all concentrations. A total of five types of CAs were observed, such as gaps, fragments, RCF, stickiness,and polyploidy. According to the present results, high concentrations of SY are genotoxic in vitro to cultured human lymphocytes. To determine its full genotoxicity potential, SY should be tested in other test systems.