Background: In Ethiopia, despite the private health sector's role in healthcare delivery is growing, studies on private health sector prescribing practices are uncommon. The main aim of this study was to evaluate the private health sector's rational prescribing practices and adherence to prescription format, using some of the World Health Organization (WHO) core drug use indicators in Addis Ababa, Ethiopia. Method: A retrospective cross sectional study design was used to collect quantitative data from prescriptions prescribed and dispensed by private health sectors in the Lemi-kura sub-city, Addis Ababa. The study was conducted from June to July, 2021. The WHO criteria were used to evaluate prescribing and prescription completeness indicators. Prescriptions, kept for the last 1-year that prescribed between January 1, 2020 to January 1, 2021 by private drug outlets, were analyzed. A combination of simple random sampling and systematic sampling procedures were employed. All the statistical calculations were performed using SPSS® V 20.0 software. Result: Off total of 1,200 prescriptions, 2,192 drugs were prescribed and the average number of drugs per prescription was 1.83 (Standard Deviation (SD)=0.9). Generic names, antibiotics, injections, and issued from national essential medicines list accounted for 77.4%, 63.8%, 11.5%, and 80.6% of all prescriptions, respectively. The patients' full names, ages, and sexes were mentioned in 99%, 95.3%, and 96.3% of prescriptions, respectively. The patient's card number (54.3%) and weight (2.3%) were not adhered to properly. The drug name, strength, dose, frequency, duration, and how to use, ranges from 85 to 99% of the prescriptions. Dosage forms (35.5%) and diagnoses (31.7%) were less likely to be completed. Only 36.6% and 25.8% of prescriptions, respectively, contained names and qualifications of prescribers. Obtaining prescription papers with the full name (9%), qualification (1.3%), and signature (26.8%) of the dispenser, and date of dispensing (0.7%), is extremely difficult. Interestingly, no dispenser filled out all of this information on a single prescription. Conclusion: The study's findings indicated rational prescribing and prescription completeness indicators were all considerably deviate from WHO standards and hence unsuitable. To promote rational medication use, health practitioners in the private sector should be given regulatory interventions, ongoing monitoring from relevant bodies, and regular training on good prescribing and dispensing practices.