Hand hygiene is important to prevent the spread of the COVID-19 virus by contact. It also interrupts the transmission of other viruses and bacteria causing common colds, flu, and pneumonia, thus useful in reducing the general burden of infectious disease. Literature shows that there is inadequate knowledge, attitude, and practice on the proper use of hand hygiene among school students. Therefore knowledge, attitude, and practice on hand hygiene of school students should be improved. Currently, different approaches are used to improve knowledge, attitude, and practice on the proper use of hand hygiene among school students. But e-educational posters are rare and the effect of e- educational posters to improve the knowledge, attitude, and practice of school students on the proper use of hand hygiene has not been studied. Therefore, the main purpose of this study was to determine the effect of an e-educational poster on improving the knowledge, attitude, and practice of the proper use of hand hygiene among school students. An interventional and prospective study was conducted on advanced-level students in Dehiovita educational zone, Sri Lanka. Pre group consisted of 405 students prior to the e-educational poster intervention. The Post group consisted of 364 subjects after being educated through e-educational poster intervention on the proper use of hand hygiene. Data analysis was conducted by using SPSS Software version 25. Students of the pre and post-groups were identical in terms of demographic variables; gender (P=0.905), subject stream (P=0.972), and grade (P=0.774). After the educational intervention, a significant improvement was established in the mean score of knowledge (P < 0.05), attitude (P < 0.05), and practice (P < 0.05) of students in the post-group compared with the pre-group. Within each group, there was no difference in knowledge, attitudes and practice attributes due to gender (p>0.05) or grade (p>0.05). However, there was an influence of the educational stream on attitude (P<0.05) and practice (p< 0.05) in pre-group as well as post-group. The influence of the educational stream on knowledge was significant (P<0.05) in the pre-group but not significant (P=0.051) in post group.