Abstract: Twenty four two-month-old virgin Sprague-Dawley rats were used to evaluate the effect of cimaterol (CIM) on growth pattern,biochemical characteristics of selected muscles and hormone level by using a pair design.Rats were alloted by weight to two groups which were ad libitum fed a diet containing 0 or 10 μg/g CIM.The experiment lasted 30 days and rats were weighted every ten days.During the experiment time 10 μg/g CIM improved growth rate and carcass yield,whereas the weight of the subcutaneous waist fat pad was decreased.The results show that CIM can significantly improve growth performance and reduce body fat content in rat.By the end of the study,compared to 0 μg/g,10 μg/g CIM significantly increased the weight and RNA concentration of gastrocnemius (fast-twitch),soleus (slow-twitch) and flexor digitalis pedis superficials (mixed) while decreased DNA concentration.As a result,the ratio of RNA/DNA of the three muscles increased significantly.This implies that the growth of the muscles is through muscle hypertrophy and the fast-twitch muscle is more sensitive to CIM.Dietary CIM also increased pituitary and serum GH content while decreased urea nitrogen level.This suggests that CIM plays its role partially by regulating the endogenous GH secretion in rat.