Abstract A cross-sectional study was conducted to assess the service quality in the Out-Patients Department of the selected base hospital in Sri-Lanka. The data were derived from 303 patients using the modified SERVQUAL questionnaire. The result provided the level of service quality at the OPD and the perception of the OPD patients' quality dimension. The results revealed that the majority of the participants were females (54.8%). The level of service quality was moderate in all the selected hospitals. According to the study domain, "Reliability "was highly correlated with {Mean; 5.5861) service quality and patients perceived law level of "Courtesy" (Mean;3.6583) in the hospitals. The monthly income of the patients influences the perception of quality. High-income patients had a higher correlation with domain "Assurance" (p=0.002) and low-income patients feel more domain "Responsibility" (p=0.002). Training programs for employees on motivation, attitudinal changes and effective communication and developing a rewarding system to strengthen service quality will improve patient satisfaction.