A nutritional survey of lactating mothers in different lactating periods was carried out in urban, suburban and rural districts of beijing in 1983-1984. Milk were collected, and its lipid compositions, including specific gravity, fat, cholesterol and fatty acids were analyzed. The results were as follows:1.The average of specific gravity of 207 milk samples were from 1.018 to 1.022. Though the value of the rural district was higher (1.022). The difference was rather small.2.216 milk samples were determined for the fat content (g%). The average of urban district was 3.78, of suburban 3.31 and of rural 3.08. Differ-eces between urban and other two districts were significant.3 .Milk cholesterol content was determined in 194 samples. The content in colostrum was the highest, 23.4mg/100g, but decreased gradually and steadied at about 10mg/100g in three months. No differece was observed among three districts.4.221 milk samples were analyzed for its fatty acid composition. The main components were oleic acid (29-37%), palmitic acid (17-25%) and lino-leic acid (12-25%), with 1-2% of erucic acid. The linoleic acid content was the highest in rural district.5.Statistical analysis showed that the correlations between milk fat and cholesterol content were significant in all the three districts, but the regression coefficient of urban district was significantly lower than that of rural district.6.There was significant correlation between fat intake of mothers and their milk fat content in total 188 samples, but no correlation was found when three districts were examined separately. All the results showed that the dietary fat intake of mothers might influence their milk fat content. The characteristics of fatty acids pattern of Chinese breast milk was the higher linoleic acid content as compared with other countries. The essential fatty acids in breast milk could meet the infant's need. The cholesterol allowance from breast milk was about 70-85mg per day.