Cyclic adenosine 3', 5'-monophosphate (AMP) phosphodiesterase inhibitors present in the culms of Phyllostachys nigra MUNRO var. henonis STAPF. and the rhizomes of Phragmites communis TRIN. (Gramineae) were identified as 2, 5-dimethoxy-p-benzoquinone, p-hydroxybenzaldehyde, syringaldehyde, coniferylaldehyde, vanilic acid, ferulic acid and p-coumaric acid. The structure-activity relationship was investigated with 12 derivatives of p-benzoquinone, 22 derivatives of benzaldehyde, 10 derivatives of benzyl alcohol, 24 derivatives of benzoic acid and 32 derivatives of C₆-C₃ related compounds.