The aim of this study was to investigate the therapeutic effects of propolis on biochemical parameters in tissues of rainbow trout (Oncorhynchus mykiss) exposed to cypermethrin. Cypermethrin is a potential toxic pollutant that directly threats the aquatic ecosystems and environment. Sublethal cypermethrin concentration of 0.0082 ppm was applied to the fish for 96 h. Propolis is a natural product collected from plants by honey bees. Its polyphenolic components, caffeic acid derivatives and flavonoids in particular, are matter of interest because of their strong antioxidant properties. Therapeutic concentration of propolis has been determined as 10 ppm in a previous study. Herein, malondialdehyde (MDA) levels and catalase (CAT) activities were determined in spleen and heart tissues of rainbow trouts. Results showed that CAT activities and MDA levels increased (P <= 0.001) in tissues of fish exposed to cypermethrin compared to control group. CAT activities and MDA levels in the tissues of fish decreased in cypermethrin+propolis group (P <= 0.001) compared to cypermethrin group. Propolis (10 ppm) on the tissues of the rainbow trout showed significant therapeutic effects. Propolis may serve as an antitoxic agent against pesticide toxicity to aquatic animals.