A new lignan glycoside, 4-O-alpha-L-arabinopyranosyl-(1' "-->2' ')-beta-D-apiofuranosyldiphyllin (2), named procumbenoside A, and 11 known compounds were isolated from the whole plant of Justicia procumbens. The structure of 2 was established by spectral analysis and chemical methods. The known compounds justicidin A (1), diphyllin (3), and tuberculatin (4) showed potent cytotoxic effects against a number of cancer cells in vitro. Compounds 1 and 4 also strongly enhanced tumor-necrosis factor-alpha (TNF-alpha) generation from mouse macrophage-like RAW 264.7 cells stimulated with lipopolysaccharide (LPS).