Low-dimensional nanomaterials (LDNs) are receiving increasing attention in cancer therapy owing to their unique properties, especially the large surface area-to-volume ratio. LDNs such as metallic nanoparticles (NPs), hydroxyapatite NPs, graphene derivatives, and black phosphorus (BP) nanosheets have been proposed for drug delivery, photothermal/photodynamic therapies, and multimodal theranostic treatments. The therapeutic effectiveness is mainly based on the physical characteristics of LDNs, but their inherent bioactivity has not been fully capitalized. In this Minireview, recent advances in the anti-cancer effects of various types of LDNs with inherent chemotherapeutic bioactivity are described and the bioactivity mechanisms are discussed on the cellular and molecular levels. BP, one of the newest and exciting members of the LDN family, is highlighted owing to the excellent inherent bioactivity, selectivity, and biocompatibility in cancer therapy. LDNs and related derivatives possess inherent bioactivity and selective chemotherapeutic effects suggesting large potential as nanostructured anti-cancer agents in cancer therapy.