The objective of the study was to evaluate the effect of chloroquine (CQ) on human lymphocytes through the Comet Assay. Lymphocytes were isolated from peripheral blood samples obtained from three healthy, non-smoking donors aged 24 to 30 years. The isolated lymphocytes were exposed for one hour to various treatments: hydrogen peroxide 2.5% (positive control), saline buffer phosphate 1X (negative control) and chloroquine at concentrations of 0 μg/ml, 0.25 μg/ml; 5 μg/ml and 300 μg/ml. The averages of the percentage of DNA in the comet tail, moment of tail and moment of Olive’s tail were recorded, with significant differences between the different concentrations of CQ (p<0.01). Also, the magnitude of DNA damage was increased as a function of the CQ concentration. The genotoxic effect of CQ was demonstrated in human lymphocytes exposed in vitro.