Upon insult, such as infection or tissue injury, the innate and adaptive immune systems initiate a series of responses to defend the body. Recent studies from immune cell-specific androgen receptor (AR) knockout mice demonstrated that androgen and its receptor (androgen/AR) play significant roles in both immune regulations. In the innate immunity, androgen/AR is required for generation and proper function of neutrophils; androgen/AR also regulates wound healing processes through macrophage recruitment and proinflammatory cytokine production. In adaptive immunity, androgen/AR exerts suppressive effects on development and activation of T and B cells. Removal of such suppression causes thymic enlargement and excessive export of immature B cells. Altogether, androgen/AR plays distinct roles in individual immune cells, and targeting androgen/AR may help in treatment and management of immune-related diseases.