The present study investigates the association between various bio-social factors that affect fertility among Dhangar tribe of Madhubani district, Bihar. The data were collected from 300 households on ever married women in the age group 15-49 years. Both bivariate and multivariate analysis has been performed to describe the fertility differentials. In Dhangars, the number of children ever born is high. The mean number of live births among married Dhangar women of reproductive age was 4 children. There are considerable differentials in the average number of live births according to women’s demographic, biological, socioeconomic,
and cultural settings. Regression analysis revealed that age of woman, maternal age at first conception, income level, ideal number of children desired, ideal number of son desired and experience of child death were the most significant variables that explained the variance in fertility. Women who considered a higher number of children as ideal, who had a
desire for son, and those who had a child death experience were more likely to have a higher number of mean live births than their counterparts. On the other hand, those who married and had their first conception at a later age, were literate, those who has a household income of more than 10000 per person and who breastfeed their children for more than 2 years had a lower number of mean live births as compared to their counterparts.