Although polymethoxyflavones (PMFs) have been reported to exhibit various pharmacological actions, the effects of PMFs sudachitin (SDC) and demethoxysudachitin (DMSDC) from the peel of Citrus sudachi on the cardiovascular system have not been clarified. This study investigated the mechanisms of vasorelaxation induced by SDC and DMSDC in rat aorta. Both compounds inhibited phenylephrine-induced contractions in a concentration-dependent manner. This was also observed in the case of KCl-induced contractions although the inhibitory effect was weak. In both contractions, no differences were found in the inhibitory effects of SDC and DMSDC between endothelium-intact and -denuded aorta. The relaxant effects of SDC in endothelium-intact aortas were not affected by L-NAME or indomethacin. In endothelium-denuded aorta, propranolol did not affect the relaxant effect of SDC. Preincubation of SDC, both forskolin- and sodium nitroprusside-induced relaxation potentiated. Furthermore, the relaxant effect of SDC was not affected by the adenylate and guanylate cyclase inhibitors (SQ22536 and ODQ). phosphodiesterase (PDE) inhibitors alone, SDC alone, and a combination of PDE inhibitors with SDC exhibited relaxant effects, while the lack of any interaction between each PDE inhibitor and SDC indicated an additive effect between the two substance categories. These results suggest that SDC and DMSDC cause endothelial-independent relaxation, and that the mechanism of vasorelaxation by SDC is associated with the enhancement of cAMP- and cGMP-dependent pathways.