The present invention relates to a gelatin derivative having an organic compound as a graft chain and a high-molecular weight micelle containing the gelatin derivative. As the organic compound, a low molecular weight compound such as succinic acid, ethylenediamine, etc., or a high-molecular weight compound such as polyethylene glycol, polylactic acid, etc. can be used. The high-molecular weight micelle can be used as a pharmaceutical composition excellent in control of sustained release or targeting property by carrying it on a drug, etc. Also, the gelatin derivative can be an excellent adhesion preventing membrane by crosslinking it.