Background: Infant mortality rate (IMR) and under five mortality rates (UFMR) are the sensitive indicators to assess health status and indicators of overall progress of a country. In India, IMR and UFMR is relatively high, and is unable to achieve the Millennium Development Goal (MDG) by 2015. Northeastern states of India depict a captivating trend in child mortality according to the report of NFHS-4 (2015-16). Therefore, the objective of this study is to estimate infant and under five mortality by place of residence and religion. In addition, to determine the factors affecting infant and under-five death. Data and Methods: This study utilizes data of National Family Health Survey (NFHS-4). Eight northeastern states and 37,167 children under-five years were included in the analysis. Synthetic cohort probability method was used to calculate IMR and UFMR. To find the nature of the association between infant and under five death with selected socioeconomic characteristics, Bivariate analysis, and Binary logistic regression were used. Result: Study revealed that children in rural areas has higher risk of infant and under five mortality. Muslims has the highest IMR and UFMR i.e. 52 and 56 per 1000 live births respectively. Adjusted odds ratio shows that wealth index, size of child, sex of child, caesarean-section delivery has impact on infant and under five death at 95% CI and p-value (<=0.05). However, in contrary with existing literature, adjusted odds ratio shows that there is negative association between age of mother, mother education, place of delivery with infant and under five death at 95% CI and p-value (<=0.05).