A new alkaloid, pipersintenamide (1), together with fourteen known compounds, have been isolated from the whole plant of Piper sintenense. The structures of these compounds were elucidated by spectroscopic analysis. Pipersintenamide, sintenpyridone, sarmentine, and 1-(3,4-methylenedioxyphenyl)-1E- dodecene at 20 μg/ml exhibited effective cytotoxicities (cell survival < 15%) against CCRF-CEM, HL-60, PC-3, and HA22T cell lines.