There is a serious problem in Japan due to vast contamination by exotic weeds causing immature compost in the forage crop fields and grasslands. It is also reported that exotic weed seed could be inactivated in compost fermentation kept more than 60℃. Hence, we investigated the effects of vacuum and heat drying, that might reach more than 60℃ of the inner temperature during the vacuum and heat drying procedure, on the viability of weed seed by Niron mesh bag method. Weed seed of 6 species mingled with cow feces were died in a vacuum heat dryer at TOKPa and 66.8℃ for 165 minutes. This result show the safety of weed seed contamination in feces drying by vacuum heat dryer.