A series of new tetrahydrobenzo[4′,5′]thieno[3′,2′: 5,6]pyrido[4,3-d]pyrimidin-4(3H)-one deriva-tives 6 have been designed and synthesized via a tandem aza-Wittig reaction. The structures of all compounds prepared have been comfirmed by 1H NMR, IR, EI-MS spectra, elemental analysis as well as X-ray diffraction analysis for 6c. Biological test showed that some of the target compounds displayed good fungicidal activity. For example, 6f exhibi...