Abstract: Eighty day old chickens were randomly divided into two groups ( n =40). The treated group was injected via sternal muscle with thymic factor D at 3 mg/kg body weight every other day from day 1 to 10, while the control group was given the same volume of sterile 0.9% NaCl. All chickens were weighed once a week from day 14 on wards. Blood samples were collected and the concentrations of thyroxine (T 4). Trilodothyroxine (T 3) and growth hormone (GH) in the plasnas were measured by radioimmunoassay (RIA). The percentage of T cells were calculated on day and 23,38. The results showed that: 1) Injection with TFD promoted growth. 2) On day 23, the percentage of T cells between treated group and controe group was significantly different ( P <0.01). 3)The concentration of T 4 between the two groups was different ( P <0.05) on day 23. The concentrations of T 3 and GH of the treated group were higher than those of the control, but the difference was not significant ( P >0.05).