SummaryTo study the effect of seed number per berry on berry ripening in highbush blueberry, self-, cross-and open pollination were carried out on 'Berkeley' and 'Dixi' in order to produce berries that contain various numbers of seeds. Seed number per berry was higher after cross-pollination than after self-or open pollination, and the number of large brownish seeds was higher than that of small white seeds after each type of pollination. Multiple regression analysis using number of large brownish seeds and small white seeds per berry as dependent variables, while days to ripening from flowering as independent variable showed significant multiple regression coefficients in all treatment on two cultivars. The standardized partial regression coefficient of large brownish seed number per berry was higher than that of small white seed number, except for self-pollination in 'Dixi'. Further, the percentage of large brownish seeds that germinated was higher after cross-pollination compared to that after self-or open pollination, and significantly correlated with the standardized partial regression coefficient. Therefore, the number of viable large brownish seeds per berry seemed to be a more important factor in determining berry ripening of highbush blueberry. Key Words：days