Insulin-like growth factor-I (IGF-I) is an important regulator of growth, development, and metabolism in animals. This study investigated its expression pattern in various tissues in Peking duck and in vivo. The result showed that the recombinant protein of IGF-I was expressed mainly in the form of inclusion bodies in the Escherichia coli cell (37.4 kD). Western blotting indicated that the recombinant protein had the antigenicity of IGF-I. Reverse-transcript PCR and real-time fluorescent quantitative PCR analyses showed that IGF-I was expressed in the heart, liver, abdominal fat, breast muscle, spleen, lung, kidney, gizzard, and small intestine of 8-week-old birds. In the RT-PCR results, IGF-I was expressed highest in the heart and lung and lowest in abdominal fat and breast muscle in male and female birds. In the real-time fluorescent quantitative PCR results, IGF-I was expressed highest in the gizzard and lowest in the lung in all ducks.