Antibiotics are the pillars of the modern medical care and play a major role in the treatment of infectious diseases where it reduced both morbidity and mortality from infections. Inappropriate use of antibiotics may fail to achieve desired therapeutic outcome which may results in the development of adverse effects and emergence of resistance. Objectives: Assessing the prescribing patterns of antibiotics in post-operated and infectious diseases and drug use evaluation using WHO prescribing indicators. Methodology: A prospective observational study carried out in departments of General Medicine, General Surgery, in Sri Lakshmi Hospital, a secondary care hospital in pileru, for a period of 6 months with a sample size of 150. Results: Out of 150 patients where post-operated patients (51%) and Infectious disease (49%). The majority of the patients prone for post-operated & infectious diseases (23%) were in age group of 21-30 years, females were more prone (57%). Most commonly affected system was gastrointestinal and respiratory system (23.3%). Among 326 antibiotic drugs, Cephalosporin’s (38.4%) are the most prescribed category of the drug. Among 150 prescriptions 40 prescriptions have drug interactions and 5 patients reported adverse drug reactions. An average of 4.75 drugs prescribed per patient encounter, the percentage of encounters with antibiotics was 24.65 %, the prescribed generic names was 90%and 98.2%antibiotics were prescribed from essential drug list (EDL) which shows deviations from standard WHO indicators. Conclusion: Prescription patterns and usage of antibiotics in this study was inappropriate in comparison of results with WHO prescribing indicators. Effective interventions are required to reduce inappropriate antibiotic prescriptions.