As a family of multifunctional cell-proliferation regulating factor. TGF-β has great potential in clinical application. Both naturaly secreted and recombinantly expressed TGF-ss are existed in the inactive form of latent complex. Activation of latent TGF-β complex is an important pathway of modulating the biological function of TGF-β. This review concerns on the molecular structure of both natural and recombinant latent TGF-β complexes, and their possible activation mechanisms under physiological conditions.