Although Tokachi district is an important upland-farming area of Hokkaido, upland crop production is very unstable due to large yearly fluctuation of humid, sub-frigid climate and wide distribution of volcanic acid soils in the district. Therefore, relationships between meteorological factors (air temperature, precipitation, and duration of sunshine) during the growing season and crop yields were analyzed, by using yield-index instead of actual yield. The yield-index is the percentage of the actual yield to the estimated standard yield, which is given by the linear regression equation between yearly yields and years.
　1) The instability of upland crops is in the order of azuki bean, wheat>soybean>kidney bean>sugar beet>soiling corn, potato.
　2) Soybean, azuki bean and soiling corn are apt to be suffered from cool summer damage, while kidney bean, sugar beet and potato from wet damage. Mean air temperature in the growing season was lower than 16.5°C in cool summer damage years, and average per month of precipitation was higher than 130 mm in wet damage years.
　Furthermore, soybean and azuki bean were affected mainly by air temperature from June to August (early growth stage and flowering stage) and soiling corn was also affected mainly by temperature of June (early growth stage). Sugar beet was affected mainly by precipitation from May to July (early growth stage and leaf-stem growing stage), and potato by precipitation of June (early growth stage).
　3) Multiple regression coefficients between yield-index and meteorological factors were from 0.83 to 0.91, and contribution percentages were from 70% to 83%. Consequently, it is thought that yield-index of upland crops can be forecasted by using the multiple regression equation from meteorological data in the growing season of each crop.