The Siberian high forms every winter with some degree of interannual variation in its location, . extent of area covered, , and intensity. The climate around Siberia is significantly affected by the expansion of the Siberian high during its mature period. An attempt was made to clarify the interannual variation of the Siberian high using monthly SLP data from the month of January from 1951 to 1990. The area over which pressure exceeded 1, 030 hPa was taken as the index of expansion of the Siberian high.<br> By analyzing the interannual variation of the Siberian high, a periodicity of 7 to 10 years was detected. It was also found that the eastward expansion of the Siberian high remained large while the extent of its westward expansion varied greatly.<br> The relationship between the east-west expansion of the Siberian high and the upper air circulation was examined. The distribution of eigenvectors 500 hPa in height with varimax-rotated EOF analysis was compared with teleconnection patterns. The first component was similar to the West Atlantic (WA) or North Atlantic oscillation (NAO) pattern and it had a high correlation with the westward expansion of the Siberian high. The second component was similar to the West Pacific (WP) or West Pacific oscillation (WPO) pattern and it was highly correlated with the eastward expansion of the Siberian high. The third component was similar to the Pacific/North American oscillation (PNA) and Eurasian (EU) patterns and it showed no correlation with the east-west expansion of the Siberian high. However, if the years of extreme east-west expansion of the Siberian high were excluded, the others correlated with the third component of EOF analysis and with the strength of the central pressure of the Siberian high. These results therefore indicate that the mechanism by which the Siberian high forms and develops is related to the teleconnection patterns of the upper air circulation.<br> In previous studies on the interannual variation of the Siberian high, the variations in intensity and position were often analyzed based on the strength of pressure at a single point. However, in this study the Siberian high was analyzed using an areal index, specifically the area in which the pressure exceeded a specific SLP value, and therefore it was possible to clarify the east-west differences in the structure of the Siberian high with respect to the upper air circulation patterns.