A series of novel 9-substituted β-carboline derivatives was synthesized from harmine and l- tryptophan, respectively. Cytotoxic activities of these compounds in vitro were investigated. The results showed that most compounds of 9-substituted β-carboline derivatives had more remarkable cytotoxic activities in vitro than their corresponding parent compounds. Acute toxicities and antitumor effects of the selected β-carboline derivatives in mice were also ...