Two new alkaloids named (3R)-3,5-bis(3-methoxy-4-hydroxyphenyl)-2,3-dihydro-2(1H)-pyridinone (1) and 1,5-dimethyl-6-phenyl-1,2-dihydro-1,2,4-triazin-3(2H)-one (2), together with two known compounds (7'R)-N-feruloyl normetanephrine (3) and N-trans-feruloyl tyramine (4) were isolated from the air-dried aerial parts of Portulaca oleracea L. Their structures and configurations were elucidated by spectroscopic methods including 1D NMR, 2D NMR, and HR-MS techniques. In addition, compounds 1-4 were tested for in vitro cytotoxic activities against human lung (K562 and A549) and breast (MCF-7 and MDA-MB-435) cancer cell lines.