All-trans retinoic acid (ATRA)-incorporated nanoparticles of methoxy poly(ethylene glycol) (MPEG)-grafted chitosan were prepared through ion-complex formation between ATRA and chitosan. This nanoparticle has around 100 nm of diameter and favorable reconstitution properties. ATRA-incorporated nanoparticles has almost similar cytotoxicity against CT-26 tumor cells when compared to free ATRA. But nanoparticles was more effective to inhibit invasion of tumor cells than free ATRA at invasion test using matrigel. These results can be explained by apoptosis analysis using flow cytometer. When free ATRA or ATRA-incorporated nanoparticles were treated, tumor cells were slight progressed apoptosis. Furthermore, apoptosis was also progressed by treated with MPEG-grafted chitosan.