Objective To study the effect of dehydroepiandrosterone (DHEA) on the immune system by measuring the apoptosis and expression of Fas/FasL mRNA of thymocytes. Methods The cell viability of thymocytes was determined by MTT assay. Thymocyte apoptosis was detected by agrese gel electrophoresis. The expression of Fas and Fas-L was analyzed by a semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method. Results DHEA decreased the cell viability of thymocytes and induced thymocytes apoptosis and increased the levels of mRNA of Fas/FasL. Conclusion DHEA can induce apoptosis of thymocytes through Fas/Fas-L pathway. It suggests that DHEA may play a role in certain autoimmune diseases related to apoptosis disturbance.