Disclosed is a novel anti-cancer agent which is less likely to be excreted from a cancer cells and is suitable for the local treatment against a cancer cell. The anti-cancer agent comprises a rotaxane compound represented by chemical formula (I) as an active ingredient. The rotaxane compound is composed of two moieties namely, a rod-like moiety having a relatively large molecule attached to each of both ends, and a cyclic moiety (a crown ether) into which the rod-like moiety has been inserted. The cyclic moiety cannot be detached from the rod-like moiety, because the rod-like moiety has a relatively large molecule attached to each of both ends and the relatively large molecules serves as a stopper for the detachment. The bond between the two moieties is not a covalent bond. Therefore, the shape of the molecule can be varied readily, and the uptake of the molecule via a receptor becomes relatively difficult. However, once the molecule is introduced into a cancer cell, the proliferation of the cancer cell can be inhibited.
