Id1(Inhibitor of differentiation-1) is a member of helix-loop-helix protein family.Early studies showed Id1 could inhibit differentiation of cells during development in normal cells.Recent findings indicated that Id1 can regulate cell cycle and promote cell proliferation.Id1 can not only affect the development in normal cells

but overexpress in many types of tumor.Id1 which is associated with degradation of extracellular matrix and tumor angiogenesis is closely related to tumor invasion.This review will discuss the role of Id1 in tumor invasion and its molecular mechanism.