The aim of this study was to evaluate the antitumor effect of combinatorial targeted therapy with paclitaxel and all-trans retinoic acid (ATRA) nanoparticles in vitro. Paclitaxel-incorporated pullulan acetate (PA) nanoparticles were prepared by the nanoprecipitation-solvent evaporation method. ATRA-incorporated nanoparticles were prepared by dialysis using a methoxy poly(ethylene glycol)-grafted chitosan (ChitoPEG) copolymer. Particle sizes of paclitaxel-incorporated nanoparticles and ATRA-incorporated nanoparticles were about 160 nm and 60 nm, respectively. Nanoparticles were reconstituted in various aqueous media such as deionized water, phosphate-buffered saline, and fetal bovine serum-supplemented cell culture media. The combination of paclitaxel + ATRA (10 + 10 μg/mL) delivered by nanoparticles showed a synergistic antiproliferative effect against CT26 cells that was not observed with other combinations. Furthermore, the activity of MMP-2, a key enzyme in tumor cell invasion, was significantly decreased in cells treated with the combination of paclitaxel and ATRA while other combinations and single agents did not significantly affect its activity. A matrigel assay supported these results, indicating that paclitaxel/ATRA combination nanoparticles are effective for the inhibition of the invasion of tumor cells. The results of the present study suggest that combination treatment with paclitaxel and ATRA could be an effective treatment for the inhibition of tumor cell proliferation and invasion, and that nanoparticles are promising candidates for antitumor drug delivery.