Methanol extracts of the rhizomes or fruit of Amomum celsum Lamxay & M.F. Newman (Zingiberaceae) yielded 5 compounds one of which, 1,3 S,5 S-trihydroxy-1-(4-hydroxyphenylethyl)cyclohexane (2), is new and one, 4-hydroxybibenzyl (1), is reported as a natural product for the first time. In addition, 3 known compounds, 5-hydroxy-3,7,3′,4′-tetramethoxyflavone (3), 3,5-diacetoxy-1,7- bis(3,4-dihydroxyphenyl)heptane (4), and 1,4-hydroquinone (5), were also isolated. Their structures were determined by performing extensive analysis of high-resolution electrospray ionization-mass spectrometry and nuclear magnetic resonance spectroscopic data. The absolute configuration of 2 was unambiguously established by X-ray crystallography and Mosher’s method. Cytotoxicity of compounds 1 and 2 against MCF-7 and Hep-G2 human cancer cell lines were tested in the sulforhodamine B cytotoxic assay. A plausible biosynthesis of 1 and 2 in A. celsum was proposed.