Background The World Health Organization (WHO) has set some standards of essential newborn care (ENC) with some activities, the implementation of which minimizes the incidence of neonatal morbidity and mortality. This study attempted to assess the practice of ENC services among nonpublic health-care facilities and determinants of adequate ENC practice in southeast Nigeria. Methods This was a cross-sectional descriptive study carried out in 4 of the largest cities in southeast Nigeria. The studied facilities were selected by purposive and convenient sampling method. Scores were assigned to the practice of ENC and computed based on standard validated criteria. Data analysis was done using Epi Info version 7.2 and statistical significance was set at P < .05. Results A total of 77 health facilities in the study area were surveyed. The mean annual birth rate in the surveyed health facilities was approximately 342.2. Majority (64.9%) of the health facilities efficiently executed 3 of the 8 ENC practices while only 27 (35.1%) facilities had good essential newborn practices score. The city where the health-care facilities were located influenced the practice of adequate ENC. A greater proportion of health facilities located in Abakaliki and Awka practiced adequate ENC compared to facilities in Enugu and Nnewi ( P = .001). Conclusion ENC service is poor in nonpublic health-care facilities in southeast Nigeria. Training and retraining of health workers as well as provision of necessary incentives through government-private partnership may help ensure better implementation of ENC in order to reduce neonatal morbidity and mortality in southeast Nigeria.