Abstract: The sex ratio (male: female 100) in Yuxi Distriet, Yunnan Province was analysed by using the data of the last national census in 1982. The following results were obtained:
1. The sex ratio of total population in Yuxi District (99. 22) was lower than that of the whole country (106. 3) , even the sex ratio in the age group of 0-4 and 5-9 years (103. 45 and 102. 90, respectively) were also lower than those of the whole country (107. 15 and 106. 24, respectively) .
2. The sex ratio of Dai ethnic group is unusually low, that of 0-14 years old being 98. 54. The sex ratio of Hui ethnic group is also low, with a value of 101. 22 for O-14 years age group, while that for Han ethnic group in the same district is 104. 16.
3. The persons born in the period of"Great Leap Forward" and“Temporal Difficulties in National Eeonomy" (aged 20-24 years) have a especially low sex ratio (92. 30) , which is the same when caleulated for different ethnic groups, or different counties, or urban and rural populations separately, and also for the whole country. It is suggested that the inerease of spontaneous abortions might be the cause.
4. The sex ratio of the total population in Yuxi District has been ever increasing steadily since the liberation, from 88. 70 in 1953 to 94. 94 in 1964, , and to 99. 22 in 1982.
5. The sex ratio of urban area (156. 48) is much higher than that of rural area (95. 86) , which is similar to the other parts of the country.

Key words: Sex ratio; Physical anthropology