For successful tissue regeneration, growth factors should be released over a long period of time at the site of action, but their in vivo half-life time is very short. The sustained release of growth factors could be achieved by taking advantage of biodegradable hydrogels prepared from acidic gelatin with an isoelectric point (IEP) of 5.0. When mixed with this negatively charged gelatin, positively charged growth factors ionically interacted at the neutral pH to form a polyion complex. Gelatin hydrogels were enzymatically degraded in the body with time and the time profile of growth factor release was in good accordance with that of in vivo hydrogel degradation. This indicates that the growth factor complexed with the acidic gelatin constituting hydrogels was released as a result of their biodegradation. This article briefly overviews the in vivo release of basic fibroblast growth factor (bFGF) and transforming growth factor β1 (TGF-β1) from gelatin hydrogels.