Background: In Indonesia, maternal mortality remains high, significantly 61.59% occur in the postnatal period. Postnatal care (PNC) provision is a critical intervention between six hours and 42 days after childbirth and is the primary strategy to reduce maternal mortality rates. However, underutilisation of PNC in Indonesia still remains high, and limited studies have shown the regional disparities of PNC in Indonesia. Methods: This study aims to explore the gaps between regions in PNC service for mothers who have had live births during the last five years in Indonesia. This study was a secondary data analysis study using the Indonesian Demographic and Health Survey (IDHS) in 2017. A total of 13,901 mothers aged 15-49 years having had live births within five years were included. Chi-squared test and binary logistic regression were performed to determine regional disparities in PNC. Results: Results indicated that the prevalence of PNC service utilisation among mothers aged 15-49 years was 70.94%. However, regional gaps in the utilisation of PNC service were indicated. Mothers in the Central of Indonesia have used PNC services 2.54 times compared to mothers in the Eastern of Indonesia (OR = 2.54; 95% CI = 1.77-3.65, p<0.001). Apart from the region, other variables have a positive relationship with PNC service, including wealth quintile, accessibility health facilities, age of children, childbirth order, mother's education, maternal occupation, spouse's age, and spouse's education. Conclusion: The results suggest the need for national policy focuses on service equality, accessible, and reliable implementation to improve postnatal care utilisation among mothers to achieve the maximum results for the Indonesian Universal Health Coverage plan.