This study tried to examine the development of civic organizations in Korea in terms of their changing membership niche. Based on the idea of Blau space proposed by McPherson (1984, 2004), we applied the theory of organization ecology (Hannan and Freeman, 1989; Caroll and Hannan, 2000) to the development of Korean civic organizations. We measured and examined the trend of niche width of civic organizations to see if growth in numbers of civic organizations was accompanied by the expansion of niche width. The results show that width of membership niche have increased in terms of occupation but not in terms of educational background. The results for the age niche are mixed in that the membership niche of labor union and vocation organization expanded while that of ryonko and religious organization shrank over time. we also calculated the degree of niche overlap over time and examined the trend. The results show non-linear trend of initial rise and slight decline toward the end of observation period. The rise of niche overlap implies that civic organizations face potential competition for recruiting members.