Leptin and its long form receptor (OB-Rb) were expressed in many tissues including mammary gland. To elucidate the expression location and relative expression quantity of leptin and OB-Rb in different development stage of mouse mammary gland, the expression and localization of leptin and OB-Rb were detected by introducing indirect immunofluorescence and laser scanning confocal microscopy. The images required were analyzed by Image Pro 5.0 Plus and the quantification of leptin and OB-Rb were represented by gray value. The results showed that leptin was detected in mammary fat pad, ductal epithelial cells and acinar epithelial cells. OB-Rb was detected on the basal surface of ductal epithelial cells and acinar epithelial cells. The expression variations of leptin and OB-Rb reached the highest level in virgin, and then decreased in pregnancy. In lactation, the expression of leptin and OB-Rb become lower. After offspring withdrew, the expression of leptin and OB-Rb increased and recovered to the original level of about virgin. The expression quantity of leptin was a little higher than OB-Rb in the whole development cycle. Correlative analysis showed that there was a positive correlation between the expression of leptin and OB-Rb(r=0.941, P≤0.01).