The purposes of this study are to clarify the regional difference of year-to-year changes of winter precipitation, and to investigate the type of disturbances contributing to winter precipitation and the relationships between the precipitation and the frequency of disturbances. First, the correlation coefficients of the precipitation for winter during forty years from 1940/41 to 1979/80 at 46 stations (Fig. 1) were calculated (Figs. 2 and 3). The area indicating the correlation coefficients above a significant level was larger on the Pacific side than on the Japan Sea side. The stations included in the semi-climatic region of the Japan Sea side (Suzuki, 1962) had similar tendencies as the Pacific side. Since the stations on the Japan Sea side correlated only to the adjacent station, on the Japan Sea side was divided into four regions; the San-in region, the Hokuriku region, the Tohoku region and the southern part of Hokkaido. On the Pacific side, the similarity of fluctuations among stations was remarkable, so the regions were not distinctly separated, but overlapped with each other. Therefore, the region west of Kanto district, the region from Kinki district to Tohoku district and the region from Kanto district to Hokkaido were combined respectively as the area having the same tendency. Daily precipitation was classified into four groups by use of synoptic charts according to the type of disturbances; Japan Sea Lows, Pacific Coast Lows, Coupled Lows and winter monsoons. The percentage ratio of the precipitation caused by lows to the total amount of winter precipitation, was calculated (Fig. 4). The same calculation was made for each type of low (Fig. 5). Moreover, the type of disturbances having a significant influence on winter precipitation and their distribution ratios were investigated for each station (Fig. 6). On the Pacific side, the disturbances contributing to winter precipitation were: Pacific Coast Lows and Coupled Lows in the south of Tohoku district, and Japan Sea Lows and Coupled Lows in Hokkaido. Though the region west of Kanto district and the Tohoku district had the same combination of disturbances, the contribution ratio between the two types of lows varied between the regions. On the Japan Sea side, likewise, the combination of disturbances and their order varied from station to station. The main causes of winter precipitation changed in accordance with the regional difference of year-to-year changes in precipitation. Correlation coefficients between the frequencies of lows in and around the Japanese Islands and the winter precipitation were calculated (Figs. 7 and 9). The winter precipitation at the stations in which lows were the main causes depended on the frequency of lows. That is, the precipitation on the Pacific side from the Tohoku district to Kyushu was related to the frequency of Pacific Coast Lows, and the precipitation Hokkaido and on the Japan Sea side of Tohoku district was related to the frequency of Japan Sea Lows (Figs. 8 and 10). We can conclude that the winter precipitation at each station mainly depends on the frequency of disturbances, and the regional differences of year-to-year changes in winter precipitation is due to the fact that the frequency of disturbances varies with regions.