Many of child sexual abuse cases had occurred in Indonesia in recent years. One of the causes of the high incidence of child sexual abuse was the absence of early sex education both in the family and at school. Sex education in children must be adjusted to the stage of child development and use methods and media that are easily understood by children. Sex education for primary school child mostly occurs in the way we talk about body parts, body function, how we teach children to care for, respect and protect their bodies, and when we prepare our children for puberty. The purpose of this study was to analyze the effectiveness of the book of sex education animated cartoons to improve the student’s sexuality understanding. The method used was quasi-experimental with a pretest posttest one group design. The analysis technique used was the comparative test with paired sample t-test. The results of this study indicated that there were differences in students’ sexual understanding before and after the application of this book. This book Using was effective to improve sex understanding of elementary school students.