Background: Respiratory tract infection is one of the problematic respiratory disease in India. Children below 5 years are more vulnerable to this disease. Mothers are primary care providers and they should have knowledge to manage respiratory tract infection. This study intended to assess the knowledge of mothers regarding prevention of upper respiratory tract infection in under five children with implementation of structured teaching program. Objective: The study was conducted with the objectives toassess the pre and post interventional level of knowledge, to evaluate the effectiveness of Structured Teaching Program and to determine the association between the levels of knowledge with selected demographic variables. Methods: The researcher used a pre experimental research design. The research approach was quantitative research approach. The study was conducted in pediatric ward at Eras Lucknow Medical College & Hospital, Lucknow. 60 sample were selected by using Non-probability purposive sampling technique. The data was collected by using structured interview schedule before and after implementation of structured teaching program. Results: The finding of this study shows that there was a significant improvement of knowledge among mothers of under five children after implementation of structured teaching program. The overall knowledge level of mothers regarding prevention of upper respiratory tract infection, in pretest there were 40 number (66.67%) of mothers with inadequate knowledge, 19 number (31.66%) of mothers with moderate level of knowledge, 1 number (1.67%) of mother with adequate knowledge where as in post-test 22 number (36.67%) of mothers had moderate knowledge, 38 numbers (63.33%) had adequate knowledge regarding prevention of upper respiratory tract infection.The post-test knowledge mean percentage was found higher (knowledge mean percentage was 78.93% with SD of 2.92 when compared with pre-test mean percentage knowledge mean percentage which was 50.77% with SD of 3.14). Knowledge mean percentage enhancement was 28.17% with SD of 2.66. The statistical paired?t test implies that the difference in the pre-test and post-test value was found statistically significant at 5% level (p<0.05) with a paired ?ttest value of 24.625. Conclusion: The overall findings of the study showed that the structured teaching program was significantly effective in improving the knowledge score of mothers of under five children regarding prevention of upper respiratory tract infection.