Children with Wilms' tumor facing many problems resulting from the disease, and its treatment. Counseling mothers of children with Wilms' tumor can enhance mother's self-efficacy to manage their children's problems and promote healthy lifestyle practices. Aim: The study aimed to evaluate the impact of counseling program on the self-efficacy of mothers to promote lifestyle of their children with Wilms' tumor. Methods: A quasi-experimental research design was utilized. Setting: This study was conducted at Oncology Outpatient Clinics in the Children's Hospital affiliated to Ain Shams University hospitals. Subjects: Purposive sampling was employed, which selected 60 mothers and their children from 3 to 8 years old. Tools: Tool (I): A structured interviewing questionnaire, composed of three parts: Part (1): Personal characteristics of mothers and their children. Part (2): Family history of disease regarding Wilms' tumors. Part (3): Knowledge of the mothers about Wilms' tumors. Tool (II): Lifestyle Assessment Questionnaire: It highlighted children's adherence with medication and therapeutic regimens, stress management, and sleep quality. Tool (III): Self-Efficacy Scale. Results: There was highly significant improvement regarding mothers knowledge, self-efficacy and their children's lifestyle practices post implementation of the counseling program with P=0.000. Conclusion: Implementation of the counseling program was effective in enhancing mothers' knowledge and self-efficacy related to Wilms' tumors as well as their children's lifestyle practices. Recommendation: Providing a continuous program in hospitals for mothers who have children with Wilms' tumors to keep them informed of health education about the care of their children.