Background and Objective: Vaccination is a cost-effective intervention to prevent major illness that leads to reducing morbidity and mortality in children. Increasing parental knowledge about regular and complete vaccination will lead to increase immunization rates. The main objective of this study is to assess the knowledge, attitude and practices regarding immunization among mothers of under five years of children. Materials and Methodology: A tertiary care hospital based cross sectional observational study was conducted over period of 2 years. Mothers of 0-60 months of children were included in study and mothers of children who were severely immunocompromised were excluded. After obtaining oral and written consent, socio demographic details were filled up and information regarding knowledge, attitude and practices was collected by using preformed structured questionnaire and child’s immunization status and perceived barriers for vaccination was also noted. Results: A total 294 mothers were included in study. In this study 68% of children were immunized age appropriately; about 30% children were partially vaccinated and nearly 2% children were completely unvaccinated. With regards to KAP score categorization in knowledge, approx. 23%, 67% and 10% mothers were having good, average, and poor knowledge respectively. Similarly, in attitude, approx. 61%, 24% and 15% were having good, average (acceptable) and poor (unacceptable) attitude respectively. However, in practice 15%, 60.5% and 24.5% mothers were having good, average and poor practice respectively. There was statistically significant association between mother’s education and socioeconomic status and practices. Conclusion: We found that majority of mothers know the importance of vaccination and has knowledge of benefits but not many of knowing details of completing schedule and many of have fear of side effects, this leads to large proportion of the children being partially immunized.