The paper aims to study the sex ratio in districts of Bihar based on decennial census report and analyze the present trend of it. Sex-ratio is one of the most significant demographic and social parameter to show the status and condition of women in the society. According to Census 2011, the sex ratio of India was 943 while it was only 918 in Bihar, which was much less than the national average, as an outcome of patriarchal society, religious belief, traditions and customs aided with modern medical technology. Bihar along with Gujarat and Jammu and Kashmir experienced low sex ratio in 2011 in comparison to 2001 The sex ratio in Bihar has constantly been declining in spite of various social, educational, economic and political developments in the society from 1061 in 1901 to 918 in 2011, which is one of the grave concern and demographic threats for the state. The declining sex ratio is an indicator of low status of female and unequal roles assigned to males and females in Bihar.