Sulfur dioxide (SO2), which is used as food preservative in apricot sulfurization and several fabricated foods, is a common air pollutant. The aim of this study was to reveal the possible genotoxic effects of SO2 using in vitro human lymphocytes. The different endpoints of genotoxicity: sister chromatid exchange (SCE), micronuclei (MN) tests and cell growth kinetics such as mitotic index (MI) and replication index (RI) were studied. The cells were treated with 0.1, 0.5 and 1.0 ppm concentrations of SO2. It was shown that SO2 caused significant increases in the frequency of SCE and MN in the middle and high dosage groups and also induced mitotic delays and decreased MI and RI. In conclusion, the results have confirmed that SO2 has potent mutagenicity and it can cause genetic damage leading to a malignancy.