Modern Postnatal Care (PNC) Services in Nigeria is a vital tool for providing quality health for mothers and newborns. Nonetheless, many Nigeria regions are still struggling to achieve optimum utilisation of Postnatal Care Services due to variations in mothers' associated socio-economic factors based on their specific locations. This study aims at assessing regional socio-economic factors associated with Postnatal Care Services utilisation and its relationship with child morbidity in Nigeria. Data for this study was extracted from the Nigeria Demographic and Health Survey (NDHS) 2018 birth recoded file dataset, with a sample size of 30,713 women (aged 15-49). Data were analysed using descriptive statistics, Chi-Square Test, and logistic regression reporting the result in odds-ratios (OR). The primary predictor variable was the region, while others included the type of Postnatal Care Services utilised and various demographic variables of the respondents – age, education, type of residence, religion, and ethnicity. The average age of the respondents was 29.5±6.8. The use of modern Postnatal Care Services ranged from South-West (20.3%), South-South (10.9%), South-East (23.0%), North-Central (22.0%), North-East (13.0%) to North-West (10.9%). The prevalence of child morbidity ranged from South-West (8.5%), South-South (9.8%), South-East (11.4%), North-Central (15.3%), North-East (26.3%) to North-West (28.7%). Child morbidity is significantly higher in the South-South (OR=1.46, 95% Confidence Interval [CI] = 1.316 – 1.611; p =0.01), South-East (OR=1.50), North-Central (OR=1.13), North-East (OR=2.31) and North-West (OR=1.35) compared to the South-West. The majority of women in Nigeria are not using modern PNC services. Regional variations in the use of PNC services and mothers' socio-demographic characteristics influence child morbidity in Nigeria. There should be region-specific sensitisation of women on the need for the benefit of modern health care for both antenatal care and postnatal care services.