Title: A descriptive study to assess the knowledge and attitude regarding optional vaccine among mothers in selected health care centres of Pune city. Objectives: To assess the knowledge and attitude of mothers of under five children regarding optional vaccine. Material and Method: A quantitative descriptive research design is used in this research study. The study was conducted in Health care centres of Pune city, India.A Non-probability Purposive sampling technique was used. Total 300 samples of mothers of under five children were included in the study. Self-structured questionnaire was prepared to assess the knowledge regarding optional vaccine. A Four Likert scale was used to assess of attitude regarding optional vaccine. Mothers filled up the knowledge and attitude questionnaire for 20 to 30 minutes. The pen and paper technique was used for data collection. The collected data were analysed by using descriptive and inferential statistics. Spearman’s correlation test was used for the correlation of knowledge and attitude of optional vaccineand Chi- square test was used to associate the demographic variables with knowledge and attitude regarding optional vaccine. Results: Data shown that majority of the mothers of under five children had adequate knowledge regarding optional vaccine 210 (70%), 70 (23.3%) had poor knowledge and only 20 (6.7%) had good knowledge. The mean of knowledge score of mother was 8.5 and SD was 2.7. Majority of the mother had positive attitude 232 (77.3%) and 68 (22.7%) had negative attitude regarding optional vaccine.The findings of the study revealed that knowledge of mothers of under five children regarding optional vaccines was having significant association with their selected demographic variables viz. age, education, type of family and family income. Conclusion: The finding of the research study revealed that this emphasizes on more responsibility of health care professionals, especially nurses in empowering the mothers of under five children with knowledge to prevent infectious diseases among children.