Chemical investigation was carried out to study the alkaloids from stems of Nelumbo nucifera and their cytotoxic activities. The constituents were separated by column chromatography, and their structures were elucidated by spectroscopic data analyses. The isolated compounds were evaluated for their cytotoxic activities by MTr method. Fifteen compounds were isolated from the total alkaloids extract and identified as asimilobine (1), isococlaurine (2), N-acetylnorarmepavine (3), crykonisine (4), velucryptine (5), pycnarrhine (6), liriodenine (7), nuciferine (8), nornuciferine (9), armepavine (10), N-methylasimilobine (11), coclaurine (12), N-norarmepavine (13), N-methylcoclaurine (14) and lysicamine (15). Compounds 1-7 and 12-15 were isolated from stems of this plant for the first time, and compounds 2-6 were firstly isolated from the family Nelumbonaceae. Compounds 7-10, 13 and 14 showed significant cytotoxic activities against HL-60 carcinoma cell line with inhibitory ratios of 51.36%, 59.09%, 52.51%, 53.93%, 51.43%, and 64.31% at concentration of 1 x 10(-5) mol x L(-1), respectively.