Abstract The objective of this study was to observe whether 1.8 GHz microwaves (MW) (SAR, 3 W/kg) exposure can influence human lymphocyte DNA damage induced by ultraviolet ray C (UVC). The lymphocytes, which were from three young healthy donors, were exposed to 254nm UVC at the doses of 0.25, 0.5, 0.75, 1.0, 1.5and 2.0 J m −2, respectively. The lymphocytes were irradiated by 1.8GHz MW (SAR, 3 W/kg) for 0, 1.5 and 4 h. The combinative exposure of UVC plus MW was conducted. The treated cells were incubated for 0, 1.5 and 4 h. Finally, comet assay was used to measure DNA damage of above treated lymphocytes. The results indicated that the difference of DNA damage induced between MW group and control group was not significant ( P > 0.05). The MTLs induced by UVC were 1.71 ± 0.09, 2.02 ± 0.08, 2.27 ± 0.17, 2.27 ± 0.06, 2.25 ± 0.12, 2.24 ± 0.11 μm, respectively, which were significantly higher than that (0.96 ± 0.05 μm) of control ( P < 0.01). MTLs of some sub-groups in combinative exposure groups at 1.5-h incubation were significantly lower that those of corresponding UVC sub-groups ( P < 0.01 or P < 0.05). However, MTLs of some sub-groups in combinative exposure groups at 4-h incubation were significantly higher that those of corresponding UVC sub-groups ( P < 0.01 or P < 0.05). In this experiment it was found that 1.8 GHz (SAR, 3 W/kg) MW exposure for 1.5 and 4 h did not enhance significantly human lymphocyte DNA damage, but could reduce and increase DNA damage of human lymphocytes induced by UVC at 1.5-h and 4-h incubation, respectively.