Delineating hospital service areas is important for planning the allocation of health care resources. This study aims to delineate Obstetric Hospital Service Areas (OHSAs)/Obstetric Hospital Referral Regions (OHRRs) by using 565,388 obstetrics medical records from 421 hospitals of Hubei Province, China, from 2016. The Huff model nested with four decay functions was used to obtain the optimal model and the probability of patients choosing hospitals was estimated. Then, the townships that were most likely to choose hospitals in the same county were aggregated into initial OHSAs/OHRRs. The initial OHSAs/OHRRs were tested by localization index (LI) and spatial adjacency to reflect their reliability. A total of 100 OHSAs and 24 OHRRs were constructed, comparable to the county and prefecture scale, respectively. The results show that the utilization of obstetric health care resources in secondary and tertiary hospitals is more efficient by OHSAs/OHRRs than by adminis-trative divisions. The OHSAs and OHRRs improve the localized medical treatment and equalization of health care resources. In conclusion, the Huff model is an effective method to delineate OHSAs/OHRRs based on the rela-tionship between supply and demand, enriching the research on HSA/HRR in China and providing a scientific reference for future planning of a hierarchical medical system.