A study to assess the effectiveness of planned health teaching programme on knowledge of mothers regarding immunization of under five children in pediatric ward of D. Y. Patil Hospital and Research Centre Nerul, Navi Mumbai. Aim: To assess pre and post-test knowledge of mothers regarding immunization of under five children in pediatric ward of D.Y. Patil Hospital and Research Centre. To find association between pre-test and post-test knowledge of mothers regarding immunization of under five children in pediatric ward of D.Y.Patil Hospital and Research Centre with selected demographic variable. Method: The research design selected for the present study was quasi-experimental one group pre-test and post-test design Non probalility purposive sampling techniques were used for the selection of 50 mothers of under five children. The tool used for data collection was self-structured questionaries, which comprised of LP items on demographic data and 25 items on knowledge regarding immunization.The reliability coefficient was found to be highly significant i.e 0.56. Results : The 50 samples, shows that majority 76% of the mothers of under five children in pre-test were having a moderate knowledge score (9-16), 12% of mothers of under five children in pre-test of study group were having adequate knowledge score (17-25) and only 0% mothers of under five children in the study group had inadequate knowledge score (0-8). The post-test majority 80% of the mothers of under five children had adequate knowledge score (17-25) and 20% of them in the post-test had moderate knowledge score (9-16). Out of 50 samples, shows that the mean pre-test score was 56.76, whereas the mean of post-test score was 74.24. Thus it can be concluded that, the planned health teaching programme regarding immunization is effective in delivering the knowledge and awareness. The present study aims to assess the effectiveness of planned health teaching programme in among the mothers of under five c