Fas, FasL and P53 are important modulators in cell apoptosis. The expression pattern of Fas, FasL and P53 proteins during the embryonic and post embryonic development of Tianfu duck thymus were studied in order to deeply understand the regulatory mechanism of natural apoptosis of thymocytes. 65 Tianfu ducks were divided into 13 groups as follows: 22, 24 and 26 days embryonic stage, and 0 (neonatal stage), 3, 5, 8, 14, 17, 20, 26, 29 and 32 weeks after hatching. Thymic tissue from each group was collected, and immediately fixed in 4 % paraformaldehyde. After fixation for 24 h, tissues were dehydrated, paraffin-embedded, sectioned at 5 μm, and stained with immunohistochemistry. Sections were observed under light microscope and microscopic analyses were performed. Results showed that Fas protein was distributed in the thymic lymphocytes (figure 1a-d). The Fas positive ratios of lymphocytes showed no significant changes during the embryonic stage (P > 0.05). However, the values increased at the neonatal stage (P < 0.05) and kept stable until 17 weeks after hatching (P > 0.05), and then showed an increased tendency from 20 to 32 weeks (table 1). The FasL protein was observed in the thymic lymphocytes and epithelial cells (figure 1e-g). The FasL positive ratios of lymphocytes presented no significant changes during the embryonic and post embryonic development (P > 0.05) (table 1). The P53 protein was expressed in the thymic lymphocytes of cortex and the epithelial cells of medulla from 8 to 32 weeks (figure 1h-k). The P53 positive ratios of lymphocytes revealed no significant variations between each group (P > 0.05) (table 2). This study indicated that Fas, FasL and P53 proteins showed different expression pattern in the development of Tianfu duck thymus.