DNA damage induced by mercuric chloride (HgCl2) and cadmium chloride (CdCl2) in Eriocheir sinensis sperms (in vitro) was studied using single-cell gel electrophoresis (SCGE). Separated DNAs were dealt with six HgCl2 and CdCl2 scalar solutions (for each) (0 mmol/L, 0.01 mmol/L, 0.05 mmol/L, 0.1 mmol/L, 1 mmol/L, 5 mmol/L) for one hour at 37 ℃ (water bath) respectively. The length of cometic tail and damage rate of DNAs were betaken as SCGE indices. Results showed that DNAs in control group are free of damage, static in electric field and manifested as a round fluorophoreu without any cometic tails. While those dealt DNAs are damaged to various degrees and demonstrated as cometic fluorophoreu in electric field after Ethidium bromide (EB) stain. Furthermore, with the incremental concentration of HgCl2 and CdCl2, damage rate and migration distance also enlarge accordingly, that′s to say, dose-response relationship exist between SCGE indices and concentration of HgCl2 and CdCl2. Therefore, it is concluded that certain concentration of HgCl2 and CdCl2 does induce DNA damage in Eriocheir sinensis sperms (in vitro) and the damage degree is related to the concentration of HgCl2 and CdCl2, which have been attested using SCGE.