Background: Stunting has a negative impact on a child's health, making them more susceptible to disease and infection, as well as their mental and physical development, making stunted youngsters less likely to reach their full height and cognitive capacity as adults. Aim: The study aimed to evaluate the effect of instructional guidelines on mothers' Knowledge and practices regarding early stunting detection among Children under five years. Setting: Maternal and Child Health Center at Kafrelsheik city. Sample: A purposive sample included 163 mothers combined with their children. Methods: Quasi-experimental design was used. Tools: First tool: Structured interviewing questionnaire was used Part I: used to assess demographic characteristics of mothers part II: Used to assess the mother's knowledge about stunting and knowledge about proper nutritional Second tool: observational checklist for assessing mothers ' practices toward growth monitoring. Results: The current study showed statistically significant differences between the mothers' total knowledge and their practices regarding early stunting detection among their children under five years pre/post instructional guidelines. Conclusion: The Guidelines were effective for the studied sample regarding early stunting detection a significant improvement was observed in the mean score and level of knowledge and practice among the studied sample in post guidelines in comparison to that in pre-guidelines. Recommendation: Conducting educational program to increase mothers' knowledge about nutritional stunting, monitoring growth & development of the child, and the benefits of early detection in treatment through mass media.