Background:: Infant mortality rate is a useful indicator of health conditions in the society, the racial and socioeconomic inequality of which is from the most important measures of social inequality.

Objectives:: The aim of this study was to determine the socioeconomic inequality and its determinants regarding infant mortality in an Iranian population.

Patients and Methods:: This cross-sectional study was performed on 3794 children born during 2010-2011 in Shahroud, Iran. Based on children’s addresses and phone numbers, 3412 were available and finally 3297 participated in the study. A data collection form was filled out through interviewing the mothers as well as using health records. Using principal component analysis, the study population was divided to high and low socioeconomic groups based on the case’s home asset, education and job of the household’s head, marital status, and composition of the household members. Inequality between the groups with regard to infant mortality was investigated by Blinder-Oaxaca decomposition method.

Results:: The mortality rate was 15.1 per 1000 live births in the high socioeconomic group and 42.3 per 1000 in the low socioeconomic group. Mother's education, consanguinity of parents, and infant's nutrition type and birth weight constituted 44% of the gap contributing factors. Child's gender, high-risk pregnancy, and living area had no impact on the gap.

Conclusions:: There was considerable socioeconomic inequality regarding infant mortality in Shahroud. Mother's education was the most contributing factor in this inequality.