This study aimed to explore the association of demographic and socioeconomic characteristics and imbalanced sex ratio at birth (SRB) in Chi Linh district, Hai Duong. The data were collected from a longitudinal study using a community-based periodic, referred as Chi Linh Health and Demographic Surveillance System (CHILILAB HDSS) during 2004 to 2013. A total of 7568 children were analyzed. Results showed that SRB in Chi Linh dramatically increased to the imbalanced sex ratio (114.6 boys to 100 girls) by 2013. SRB was associated with birth order and sex of preceding siblings. SRB was extremely high among families without any sons (136/100). SRB was highest among families having third or more children (175/100). Imbalanced SRB was more likely to occur among women working in small business/homemakers and others, women who attained high education level, and women in wealthy households. We suggested further efforts to tackle imbalanced SRB in periurban areas in Vietnam.