A new 1-azaanthraquinone, named laoticuzanone A (1), and a synthetically known 3-methyl-1H-1-azaanthracene-2,9,10-trione (2), together with four known compounds, Griffithazanone A (3), methyl sinapate (4), methyl p-coumarate (5), and p-hydroxyphenylethyl p-coumarate (6) were isolated from the stems of Goniothalamus laoticus. Their structures were established on the basis of spectroscopic data as well as comparisons with the previous literature data. Compound 1 showed the highest cytotoxicity against KB and HeLa cells with IC50 values of 0.68 and 0.50 μg/ml, respectively.