Background: Postnatal care service is a key to achieving the Sustainable Development Goals (SDGs), especially goal number three and its targets to reduce maternal mortality rate and ending preventable deaths of newborns. Nevertheless, its utilization and adherence have been unsatisfactory and subjected to a wide range of factors, that have a substantial impact on the thrives of maternal and neonatal mortality as well as morbidity, which remains a challenge to overcome. Objective: This study aimed to determine the factors associated with puerperal women's adherence to the utilization of post-natal care services in Moshi Municipality, Tanzania. Materials and methods: An exploratory descriptive research design was used at the outpatient infant immunization clinics of four selected health facilities representing Moshi municipality. A convenient sample of 360 women attending the selected settings were proportionally recruited according to the inclusion criteria. Results: Adherence to the utilization of postnatal care services was found to be 25.3%. Factors like receiving information about puerperium (0.000), place of delivery (p=0.023), receiving health education on postnatal visits (p=0.000), availability of transportation (p=<0.00001), receiving information about postnatal visit schedules from health personnel (p=0.001), waiting time at a health facility (0.001), methods of payment for hospital bills (p=0.004), initiation of seeking postnatal services (p=0.024), and provision of postnatal care by health personnel (p=0.007) were significantly associated with adherence to the utilization of postnatal care services among puerperal women. Conclusion: Adherence to the utilization of postnatal care services in Moshi municipality was very low and significantly associated with some reproductive, and health services utilization-related factors. Recommendations: The responsible authority should encourage continuing health services throughout the maternity cycle and using postnatal care services based on the recommended schedule.