Pacific white-sided dolphins (PWSDs) are small-sized cetaceans frequently observed around the coastal waters of Japan. They seasonally shift in distribution that moves northward in summer and returns southward in winter. Sighting surveys conducted around the Japanese waters illustrate their distribution and occurrence in most months of a year, whereas records on their winter distribution are vacant due to the restrictions on extreme marine conditions. To fill the gaps in PWSD’s winter distribution, visual surveys of marine mammals were conducted from the R/V HAKUHO MARU (JAMSTEC, 3991 gross tonnages) in December 2020 in the northern waters of Japan. A total of 413 individual PWSDs in 15 groups were observed in the Eastern Honshu mixed waters along the North Pacific side and in the Tsugaru Strait vicinity waters of the Japan Sea. SST corresponding to PWSD’s distribution showed no significant difference between the Japan Sea and the North Pacific side. PWSDs were observed in SST ranged from 11.3℃ to 13.4℃ across the entire surveyed areas, which are consistent with their common inhabiting water temperatures. Our observations recorded PWSD’s winter distribution in the northern waters of Japan for the first time, which will further help to understand their spatial and temporal movement patterns.