Objectives: About 80% of pharmaceutical marketing efforts are directed toward physicians who are important decision-makers to patients’ medication needs. Pharmaceutical marketing can affect drug prescriptions, which, in turn, may adversely impact prescription practices. This study investigated the effect of pharmaceutical promotions on the antibiotic prescribing behavior of private practice physicians. Materials and Methods: A cross-sectional and descriptive design was employed. Self-administered questionnaires, scaled on a linear 5-point Likert Scale, were distributed among 268 physicians attending the 44th annual scientific conference of the Association of Nigerian Private Medical Practitioners at Ibadan, in Southwest Nigeria. Results: The study achieved a response rate of 94%, and 243 completely filled questionnaires were included for data analysis using R version 4. Cronbach’s alpha reliability of the research instrument was found to be 0.991, indicating an excellent internal consistency. Most of the physicians were male (71%), medical officers (83%), and 49% were between the ages of 51 and 60 years. About 65% had over 20 years of practice experience. A majority, 211 (87%), have prescribed antibiotics under the influence of pharmaceutical companies’ promotions. However, Fisher’s exact tests demonstrated a weak association between relevant independent variables and the dependent variable (P > 0.05). Conclusion: Product detailing by pharmaceutical sales representatives was the most popular form of promotion and company-sponsored presentations had the greatest influence on the physicians’ prescription practice. It is, therefore, recommended that pharmaceutical promotions should be well regulated to guard against unethical practices.