From 1994 to 1966, monitoring sensitivity to diethofencarb mixtures (diethofencarb+thiophanate-methyl and diethofencarb+procymidone) was undertaken on 2, 519 isolates of Botrytis cinerea collected from 208 fields of cucumber, tomato and other crops in Kanto-Tosan district. The result revealed that resistant strains to diethofencarb mixtures were distributed widely in this district. The frequency of the resistant strain increased year by year and reached 60% of all isolates. However, most of the resistant strains were benzimidazole highly resistant and diethofencarb weakly resistant (HR·WR). The high frequency of the resistant strain was observed in the fields where diethofencarb mixtures had been used intensively.