In order to investigate the chemical constituents and biological activities of Alstonia macrophylla, six monoterpenoid indole alkaloids,namely vallesamine (1),picrinine (2),khasuanine A(3),scholaricine(4),echitamine(5),strictosamide(6) were isolated from leaves and twigs of Alstonia macrophylla by repeated column chromatography over silica gel,Sephadex G and Prep-HPLC.Their structures were elucidated based on NMR and MS spectroscopic data.Compounds 3 and 6 were firstly obtained from this genus,and compounds 1,2,4 and 5 were isolated from this plant for the first time.All compounds were evaluated the cytotoxicity of HCT-116 and DLD-1.Among them,compounds 2 and 4 had certain cytotoxicity,and compound 4 showed DLD-1 inhibitory activity with an IC₅₀ value of 16.7 μg/mL.