structure–activity relationships of novel naphthalimide derivatives bearing disulfide bond toward antitumor activity, we prepared a series of those and their in vitro antiproliferative activities were screened against human cancer cell lines A549, Hela, SMMC-7721, and normal cell lines L929 by CCK-8 assay. After testing, most of synthesized compounds 5a-i, 6a-i showed better antitumor activity than the positive