Abstract: In order to find compounds with higher fungicidal activity and analyze the structure-activity relationship of spirocyclic butenolide compounds, a series of novel spirocyclic butenolide derivatives containing fused heterocyclic moiety such as imidazo2,1-bthiazol-5(6H)-one, imidazo2,1-b1,3thiazin-3(2H)-one and imidazo 2,1-b1,3thiazine-3,6(2H,7H)-dione were designed and synthesized using spirocyclic butenolide as the orientation structure. Their structures were characterized by ¹H NMR, ¹³C NMR and HRMS spectral data. The in vitro fungicidal activity evaluation results showed that the EC₅₀ values of compounds 5f and 6f against Sclerotinia sclerotiorum were 33.2 and 29.8 mg/L, respectively, which were better than that of the commercial fungicide fenamidone (46.8 mg/L). While the EC₅₀ values of compounds 7b and 7e against Phytophthora capsici were 45.8 and 43.5 mg/L, which were also better than that of fenamidone (50.7 mg/L). Comparison with lead compounds, their fungicidal activities were higher than that of 2-methylthio analogues and lower than that of 2-arylamino analogues, which indicated that introduction of the fused heterocyclic moiety can improve the fungicidal activities, and the NH group in the structure play a key role in the fungicidal activity.