Background: The phenomenon of smartphone misuse in children is not only related to the use of smartphone that are getting earlier but also the high duration of smartphone usage and exceeding recommended usage limits. The use of smartphone can make children dependent because it have a pleasant effect and make children avoid conflict. Aim: assess mother's awareness of misuse of smartphone by their children under five years.  Design: A descriptive design was utilized to achieve the aim of this study. Setting: (Maternal and Child Health Center) in Bab Al Sharia, west of Cairo governorate,  (Maternal and Child Health Center)  Seventh District,  in Nasr City, east of Cairo governorate, (Maternal and Child Health Center) Egyptian Gulf in the Dome Gardens, north of Cairo governorate (Maternal and Child Health Center)  Ancient Egypt in the Sayeda Zeinab, south of Cairo governorate. Sample: Purposive sampling technique of 266 mothers was used according to equation. Tools: two tools were used, first tool A Structured interviewing questionnaire sheet It  included three parts, Part 1: mother's and child Socio- demographic data,  Part 2: Mother's knowledge related to the misuse of smartphone by their children under five years Part 3: Mother's reported practices related to avoiding Health problems of smartphone misuse, second tool Attitude Rating Scale" Likert Rating scale" adopted from (Batterton, & Hale,  2017) for assessing mothers attitude regarding to smartphone misuse by their children under Five years of age. Results: Findings of the present study showed that (60.2%) of the studied mothers had unsatisfactory level of knowledge, (57.8%) of the studied mothers had unhealthy level of reported practices, and (54.5%) of the studied mothers had negative level of attitude. Conclusion: there was no significant statistical relation between total level of knowledge and total level of practice among the studied mothers and there was no significant statistical relation between total level of knowledge and total level of attitude among the studied mothers. While there was a significant statistical relation between total level of attitude and total level of practice among the studied mothers. Recommendations Health education and training programs are recommended to increase mothers' awareness (knowledge, attitude and practice) about smartphone and negative effects of technological devices. Booklets with illustrated pictures about smartphone addiction and it's prevention among preschool children should be available at nursery schools. Formulate strategies to reduce indiscriminate smartphone use by mothers and help them use smartphones