①Twenty 240 d old Yuehuang hens were equally divided into 2 groups and respectively inoculated I.m. with recombinant leptin or BSA immunogen (containing 1 mg protein in 1 mL mineral oil emulsion adjuvant, n=10 in each group) on days 3, 31, 63 and 84, blood sampled on days 1, 31, 53, 78 and 91 in the experiment. The plasma anti-leptin antibody titres following 1st inoculation became significantly (P<0.01) higher than in the control hens, so were plasma leptin levels，which steady increased following repeated immunizations. Plasma total T3 and total T4 levels were slightly lower but not significantly different (P>0.05) in treated hens following repeated inoculations from levels in control hens. The laying rates was significaltly depressed (P<0.05) by leptin immunization by 50% after the 3rd inoculation. Feed intake was slightly lower whereas live weight slightly higher in leptinimmunized than in the control hens. The abdominal fat mass was significantly higher in treated than in control hens (115.60±15.07 g vs 77.98±5.70 g,P<0.05) on day 98. ②Twelve 50 d old pullets were I.m. injected with anti-Leptin antibody in yolk extracts (n=6) or physiological saline (n=6). Pullets passively immunized against Leptin exhibited significantly higher (P<0.05) accumulative feed intake at 2, 4 and 6 h post injection than the saline injected controls. However the total feed intake of the 2 groups were identical at 8 h postinjection (P>0.05). The above results mimicked the biological effects of loss of leptin bioactivities observed in mammals and implied correctness of so far cloned chicken leptin gene, therefore contributed to clarify the disputes regarding this gene.