Different beta 1 and 2 adrenergic receptors agonists might have various biological and physiological effects on fish species. An experiment was designed to study the effects of feeding ractopamine, terbutaline and metaproterenol; as beta1, beta2 and less selective beta2 adrenergic receptor agonists, respectively; on body weight gain, feed conversion rate, concentration of biochemical parameters in the serum, gene expression of carnitine palmitoyltransferase I in liver and meat and also, fatty acids profile of filet of the rainbow trout. One hundred ninety two juvenile rainbow trout were randomly assigned into 16 fiber glass tanks and fed one of four dietary treatments containing control (0), ractopamine, terbutaline and metaproterenol at level of 10 ppm in diet for 8-week feeding trials. The results showed metaproterenol and ractopamine improved final body weight, body weight gain and feed conversion rate of fish. The serum concentrations of phosphorus and albumin were also significantly increased by all beta adrenergic agonists and ractopamine reduced triglyceride level (p<0.05). The fatty acids level of fish filet was significantly increased by the dietary supplement of various beta adrenergic agonists (p<0.05) but ractopamine had a greater effect. The gene expression of carnitine palmitoyltransferase I in liver was significantly (p<0.05) increased by all beta adrenergic agonists. The present study showed that various beta1 and beta2 adrenergic receptor agonists had same physiological effects on rainbow trout but it seems ractopamine, as a beta1 adrenergic receptor, had more potential on fatty acid metabolism and growth response of rainbow trout.