A series of novel bivalent β-carboline derivatives were designed and synthesized, and in vitro cytotoxicity, cell apoptosis, and DNA-binding affinity were evaluated. The cytotoxic results demonstrated that most bivalent β-carboline derivatives exhibited stronger cytotoxicity than the corresponding monomer against the five selected tumor cell lines (A549, SGC-7901, Hela, SMMC-7721, and MCF-7), indicating that the dimerization at the C³ position could enhance the antitumor activity of β-carbolines. Among the derivatives tested, 4B, 6i, 4D, and 6u displayed considerable cytotoxicity against A549 cell line. Furthermore, 4B, 6i, 4D, and 6u induced cell apoptosis in a dose-dependent manner, and caused cell cycle arrest at the S and G2/M phases. Moreover, the levels of cytochrome C in mitochondria, and the expressions of bcl-2 protein, decreased after treatment with β-carbolines, which indicated that 6i and 6u could induce mitochondria-mediated apoptosis. In addition, the results of UV-visible spectral, thermal denaturation, and molecular docking studies revealed that 4B, 6i, 4D, and 6u could bind to DNA mainly by intercalation.