Return periods of continuous snow cover duration at the 24 observation points in Hokkaido were investigated using the Weibull distribution method. The mean value of continuous snow cover duration was in the region of 120 days to 170 days. The differences between the mean value and the value of return periods of continuous snow cover duration at 3, 5, 10 and 30 year intervals were about 7, 14, 21 and 30 days, respectively. The differences between the mean value and the first date of the return periods of continuous snow cover duration at 3, 5, 10 and 30 year intervals were about 6, 10, 15 and 23 days. In the same, the last date of continuous snow cover duration at 3, 5, 10 and 30 year intervals were about 4, 8, 10 and 14 days, respectively. The variation of the return periods of last date was small compared with the first date.