From the methanolic extract of the leaves of Boenninghausenia albiflora MEISSNER var. japonica S. SUZUKI, a new coumarin, named matsukaze-lactone (I), C₂₀H₁₄O₆, m.p. 267∼268°, was isolated. Methylation of I with dimethyl sulfate and methanolic alkali gave an acid (IIa), C₂₂H₂₂O₈, which was oxidized to an acid (IIIa), C₁₈H₁₈O₈. By decarboxylation of IIIa with copper powder, 2, 2', 4, 6'-tetramethoxybiphenyl (V) was obtained. From these results, the structural formula (Ia), (Ib) and (Ic) were proposed for matsukaze-Iactone.