Emamectin, a neurotoxic agent, is a semi-synthetic insecticide that belongs to the Avermectin family and is used against helmintic infections in the Salmonidae family. Its secondary effects are not clear; thus, the aim of this study was to investigate the only effects of emamectin benzoate on various biochemical parameters (AST, ALT, GGT, total protein, albumin and glucose) in serum and expressional changes of IL-1 beta, TNF-alpha, HSP70 and IL-8 in liver and spleen. For the purpose stated above, rainbow trout (n = 15) were administered 50 mu g EB per kg fish daily for 7, 14 and 21 days. The results indicated that weight gains did not change (p > 0.05), AST increased at day 21 (p < 0.05), while the changes of other biochemical parameters were not significant (p > 0.05). The changes in expression of IL-1 beta, TNF-alpha and HSP70 were significant (p < 0.05), while the changes of IL-8 expressions were not significant (p > 0.05). In a conclusion, EB changed immun and stress-related gene expression in liver and spleen, and furthermore, AST changed in a dose- and time-dependent manner. The results imply that emamectin benzoate cause stress. This study is helpful to understand the effects of avermectin pharmaceutical family.