Background and aim: Colostomy is a surgical procedure that involves creating an opening in the abdominal wall to divert the flow of stool from the colon to a stoma. This procedure can have a profound impact on the lives of pediatric patients and their families, requiring specialized care and support. Therefore, this study aimed to evaluate the effect of Nursing Instructions on Mothers' Knowledge and Practice of Colostomy Care. Methods: A quasi-experimental design was used. A purposive sample of 60 mothers of children with colostomy was selected from the pediatric surgical unit at Cairo Specialized Pediatric Hospital. first 30 mothers considered control group and second 30 mothers considered as the study group, two tools were used a structured interview questionnaire and mothers' knowledge and observational checklist regarding colostomy to collect data, Results: There was a statistically significant difference between the study and control groups regarding knowledge and practice total mean scores (p < 0.005), with higher total mean scores in the study group than in the control group. Conclusion: mothers who receive nursing instruction related colostomy care have higher mean score of knowledge and practice than mothers who receive hospital routine care.