The objective of this study was to determine effects of active immunization against the recombinant second extracellular loop of sheep β₂-adrenoceptor (rBAR) on growth performance, carcass parameters, internal organ weight, and some blood biochemical parameters of rats. Forty five six-week-old female Wistar rats were randomly allocated to three groups and received active immunization of rBAR (rBAR-immune group) or adjuvant by subcutaneous injection (contol goup), or oral administration of β-agonist clenbuterol hydrochloride (clenbuterol goup). Results showed that active immunization against rBAR displayed significant antibody titer responses. Growth performance, feed intake, carcass weight and leg muscle weight of rats were increased by oral administration of clenbuterol (P<0.05), but not by rBAR immunization. rBAR immunization increased weight of liver and lungs, and decreased blood urea nitrogen and triglycerides of rats (P<0.05). Abdomen fat weight and concentration of total cholesterol tended to decreased by rBAR immunization (P=0.11 and P=0.087). The results implied that antibody raised against the recombinant second extracellular loop of sheep β₂-AR can mimic part functions of β-agonist.