BackgroundSex preference is one of the cultural problems of countries in the field of demographic issues. It can increase the number of pregnancies, reduce the interval between births and delay in seeking prenatal care, which can threaten the health of mother, baby, child and family, especially in traditional societies.ObjectivesTo determine the role of ethnicity on sex preference of different ethnicities living in North Khorasan Province (Iran).MethodsThis cross-sectional study was conducted using a multistage cluster sampling method and a researcher-made questionnaire of reproductive behavior on 1,000 women from 5 ethnicities (Fars, Turk, Kurd, Turkman and Tat) in North Khorasan Province in the summer of 2016. Data were analyzed by IBM-SPSS version 21, using descriptive statistics, ANOVA, t-test, and logistic regression. A significance level of ≤0.05 was set for examining the study hypotheses.ResultsThe results showed sex preferences among different ethnicities of North Khorasan Province. The highest level of preference for sons was seen in Turkman (66% vs. 23%). Unlike other ethnic groups, Turkman (21%) and Kurdish people (29.7%) were under pressure from the spouse’s family to give birth to sons.ConclusionSex preference, especially among the Turkman ethnic group, which are different in terms of geographical, economic and social conditions, affects the fertility and reproductive behavior of the respondents; and it is necessary to reduce son preference for the health and well-being of children and women.