Induction of heat shock proteins (hsps) is considered as an important protective, ecophysiologically adaptive, and genetically conserved response to environmental stress in all organisms. The effects of exposure to sublethal doses of CdCl2 (0.05, 0.1 and 0.2 LC50) during 14 days on mRNA-hsp70 expression in liver and gillwere investigated in juveniles of Persian sturgeon (Acipenser persicus). First, a fragment of 726 nucleotides coding for hsp70 was cloned from the liver. The result showed that in both study tissues, gill and liver, the relative mRNA-hsp70 expression level significantly increased (p≤0.05) on all study days compared to control group. Relative mRNA-hsp70 showed a clear time- dependent response in both tissues following the exposure to CdCl2. A significant increase (p≤0.05) was observed on the second day and then decreased up to day 7 of the exposure and increase level of mRNA-hsp70 expression was observed on day 14. The same trends were observed on all the study doses (0.05, 0.1 and 0.2 LC50), in both examined tissues. Although in this study up expression of hsp70 was common to both the gill and the liver, it was significantly (p≤0.05) expressed more in the liver than the gill. At higher dose, the increase level of mRNA expression was found to be more than that of other experimental doses in all study days. The result revealed that these proteins can be used as a promising biomarker for Cd contamination in this species.