Objective: Drug-related problems are a common health problem in hospitalized patients, affecting optimal patient outcomes. The aim of the study is to classify the drug-related problems detected by clinical pharmacy resident in hospitalized patients during their rotations and evaluate their interventions to the healthcare team. Material and Method: This is a retrospective study in which the drug-related problems of the patients hospitalized in the internal medicine wards between April and November 2018 were examined during the rotations of the clinical pharmacy resident. Patients’ demographics, prescribed medicine, laboratory findings were recorded. Drug-related problems are classified with the Pharmaceutical Care Network Europe Version 9.1 system. Result and Discussion: Ninety-two patients were included in the study. The median age of patients was 60.5 years and 59.8% of them were female. Most of the patients (63%) had three or more comorbidities. The most frequent comorbidities were hypertension (21.70%) and diabetes mellitus (10.64%). One hundred forty-seven drug-related problems were detected in 57 patients (62%). Potential drug-drug interactions (55.78%), errors in dosing timing instructions (9.52%), and inappropriate drug use according to guidelines (8.16%) were the most common causes of drug-related problems. The acceptance rate of interventions for resolving drug-related problems was 65%. The most common drug-related problems in this study were due to drug selection. The acceptance rate of recommendations for drug-related problems was lower than in the literature. However, this initial acceptance rate can be considered successful in a center where clinical pharmacy services have not been established.