ABSTRACT Gibberllin A 3 is a plant growth regulator hormone used to increase the growth and flowering of fruits and vegetables. In the present work, the cytogenetic effect of different concentrations of gibberellin A 3 (0.1, 0.5, 1 and 2 mg) was studied in human lymphocyte culture. Treating cultures with gibberellin A 3 induced chromosomal aberrations, sister chromatid exchanges and DNA damage. The chromosomal aberrations include gap, break, deletion and centromeric attenuation. DNA damage was detected by comet assay and by total genomic damage method using gel electrophoresis. By increasing the concentration of gibberellin A 3 , the number of damage cells and the damage DNA spots increase. Moreover, the gel electrophoresis method showed that there was an increase of released DNA and RNA as the concentration of gibberellin A 3 increase. Green tea (Camellia sinensis) is one of the most popular bervages consumed. Green tea and its constituents were found to have a variety of therapeutic effects. The results obtained in the present investigation showed that when green tea and gibberellin A 3 were simultaneously applied in the culture media, the mutagenic changes induced by gibberellin A 3 were significantly reduced