The objectives of the present study were to investigate the effects and mechanisms of lysine on sheep performance. Fifteen sheep of 1 year old around were divided into 3 groups. Sheep in groups A, B and C were fed basal diets supplemented with 0, 4 and 10 g lysine, respectively. All sheep were slaughtered to collect the samples of liver and longissimus dorsi muscle on day 28. Total RNA was extracted from the tissues, and then IGF-Ⅰ and GAPDH genes were amplified by RT-PCR after reverse transcription. Finally, the expression of IGF-Ⅰ mRNA in liver and longissimus dorsi muscle was analyzed by real time PCR. Results showed relative expression of IGF-Ⅰ gene in group C was significantly higher than that in group B (P<0.01) and relative expression of IGF-Ⅰ gene in group B was significantly higher than that in group A (P<0.01). It was concluded that adding a certain quantity of lysine could regulate growth and development of tissue in sheep.［Chinese Journal of Animal Nutrition, 2010，22（2）:487-491］