Pharmacovigilance (PV) is the science and activities related to the detection, assessment, understanding and prevention of adverse effects. Healthcare professionals (HCPs) have an important role in reporting Adverse Drug Reaction (ADR) cases. However under-reporting has been a major challenge in PV. Hence, we assessed the knowledge, attitude and practice (KAP) of HCPs about PV in a tertiary hospital of Kathmandu. A cross-sectional study was conducted using pretested questionnaire consisting of 21 closed ended questions (twelve on knowledge, five on attitude, four on practice and one open ended question to know the causes of under-reporting. Out of 520 HCPs, 448 (207 doctors and 241 nurses) participated in the study with the response rate of 86.2%. The mean KAP score for doctors was 10.38 ± 2.68 and 9.60 ± 2.32 for nurses. The major barriers for under-reporting were identified as the difficulty in deciding if it’s an ADR and lack of time to report ADRs. No significant correlation between knowledge and attitude of the HCPs was found (r=0, n=448, p< 0.01). However, there was a weak positive correlation between knowledge and practice (r= 0.05, n=448, p< 0.01) and also for attitude and practice (r= 0.09, n=448, p< 0.01). Hence, the HCPs had poor knowledge and practice but positive attitude towards PV. It is therefore strongly recommended to have an immediate educational intervention among the HCPs to improve the spontaneous ADR reporting.