Two types of innate immune receptors, pattern recognition receptors, and resistance proteins, play crucial roles in plant innate immunity; however, the molecules activated by the receptors and how immune responses are transmitted are not well understood. Evidence has been accumulating for a decade that Rac, a small guanosine triphosphatase (GTPase; also known as Rop) belonging to the Rho-type small GTPase family, is a key regulator of innate immunity in rice, barley, and other species. Like other small GTPases, Rac GTPases function as molecular switches by cycling between GDP-bound inactive and GTP-bound active forms in cells. Rac GTPase acts as a key signaling switch downstream of the two types of immune receptors and triggers innate immunity. This review outlines the role of the Rac family small GTPase and its associated proteins in rice innate immunity.