Detailed Climatic Classification of Tohoku district is obtained by principal component analysis using climatic elements at 242 places.Climatic elements are 11 as follow (numbers in parentheses are years of observation);X1: Monthly mean temperature at sea level, during May-Oct. (1931-60).X2: Monthry mean temperature at sea level, during Dec.-Mar. (1931-60).X3: Monthry mean diurnal range of temperature, during May-Oct. (1931-60).X4: Monthry mean diurnal range of temperature, during Dec.-Mar. (1931-60).X5: Total precipitation, during Apr.-June (1061-70).X6: Total precipitation, during July-Sep. (1966-70).X7: Monthly mean of daily minimum humidity, during Dec.-Mar. (1966-70).X8: Monthly mean of daily minimum humidity, during Apr.-June (1966-70).X91: Monthly mean of daily minimum humidity, during July-Sep. (1966-70).X10: Maximum depth of snow cover (1935-44).X11: Duration of continuous snow cover (1935-44).Highly significant correlatiion is found between maximum depth of snow cover and duration of continuous snow cover, and is found between spring humidity and summer humidity. Also, high significant correlation is found between temperature of warm season and winter temperature, is found between spring precipitation and summer precipitation, and is found between winter humidity and duration of continuous snow cover (shown in Table. 1).4 principal components are obtained in greater order (shown in Table. 2). But the contributory rate of the forth principal component is small and geographical distribution of scores are random, so this component is of no use for the classification.The first principal component is put together chiefly in information of climatic elements of winter, snow cover, humidity and temperature. And this geographical distribution is shown in Fig. 1.The second principal component is put together chiefly in information of humidity and temperature of warm season, and this geographical distribution is shown in Fig. 2.The third principal component is put together chiefly in information of precipitation of warm season and annual temperature, and this geographical distribution is shown in Fig. 3.Further, accumulated contributory rate of these three components is 71 percent.Three-dimensional space, which is made from those components meeting at right angles, is divided in 14 groups (namely 14 climatic types), and mean scores of groups and distance of each group are shown in Table. 3. Roman numerals of group names are distinguished by score's sign of the first and second principal components. English characters are distinguished by score's sign of the third principal component, and subscript numbers are small classifications.Those climatic types are plotted on the map of Tohoku district, and the map is divided into 21 small climatic areas. Also, 21 areas are united 9 zones (shown in Fig. 5).