Phytochemical investigation of the whole plant of Andrographis viscosula has led to the isolation of three new 2'-oxygenated flavonoids, (2R)-5-hydroxy-7,2',3'-trimethoxyflavanone (1), 7,2',5'-trimethoxyflavone (2), 5,7,2',3'-tetramethoxyflavone (3), and eight known flavones, 5,7,2'-trimethoxyflavone (4), 5,7,2',4',5'-pentamethoxyflavone (5), echioidinin (6), 5,2',6'-trihydroxy-7-methoxyflavone (7), 5-hydroxy-7,2'-dimethoxyflavone (8), echioidin (9), echioidinin 5-O-glucoside (10), and 5,2',6'-trihydroxy-7-methoxyflavone 2'-O-glucoside (11). The structures of 1-11 were elucidated by physical and spectral methods, including extensive 2D NMR studies. The presence of 2'-oxygenated flavonoids is apparently restricted to Andrographis species in Acanthaceae. Therefore, 2'-oxygenated flavonoids are regarded as chemotaxonomic markers of Andrographis genus in the Acanthaceae family.