Based on the 1980 and 1990 STFIA data, the average residential segregation level (measured by index of dissimilarity) among 13 ethnic categories (Chinese, the Filipino, Japanese, Asian Indian, Korean, Vietnamese, Mexican, Puerto Rican, Cuban, non Hispanic white, non Hispanic black, Hispanic White and Hispanic black) declined from 0.58 to 0.56 on the census tract level in Los Angeles County. It increased slightly, however, from 0.32 tp 0.33 on the city/CDP level. Blacks, including non Hispanic blacks and Hispanic blacks, were the most segregated categories on both geographic levels in 1980 as well as 1990. Nevertheless, their average segregation levels had declined most rapidly among the 13 ethnic categories on census tract level. As found by previous researches, all Asian groups were highly segregated from blacks on both georaphic levels while their residential dissimilarity with whites increased significantly only on the city/CDP level. This might indicate that different ethnic groups were on the one hand clustering in certain larger geographic enclaves, and on the other hand integrating with other ethnic groups locally. A multiple regression was also applied to explain the residential dissimilarity of minorities with non Hispanic whites. Both the minority's average family income and their average ethnic prestige score had a significant impacts on such dissimilarity.