The present invention relates to polymeric antitumor agent which is formed in polymeric micelle complex by intermolecular bonding or mutual interaction between styrene maleic acid copolymer (SMA) and low molecule antitumor agent which is anthracyclins drug such as pirarubicin, doxorubicin, epirbicin, daunorbicin, acralbicin, or alkaloid antitumor agent such as cis-platinum, and taxol. These polymeric antitumor agents may improve specificity to cancer cells so that it improves antitumor effect, while it may not be concentrated at normal organ or tissue, so that adverse effect may be diminished. These polymeric antitumor agents may be prepared by dissolving SMA and low molecule antitumor agent in aqueous solution, then in the presence of aqueous soluble carbodiimide, amino acids, or polyamine, adjusting pH to form micelle complex and recovering polymer fraction.
