Objectives Parents play a significant role in promoting of healthy sexuality in adolescents. The purpose of the present study was to assess the effectiveness of a sexuality education intervention program to enhance parent–adolescent sexual communication. Methods This study was a randomized controlled field trial. Parents of male adolescent aged 13–16 years were recruited from eight public all-boys high schools in Karaj, Iran. A multi-stage stratified random sampling method was used and 102 parents were assigned into intervention and control groups. The recruitment and data collection process lasted from February to November 2019. Self-report demographic questionnaire and six general parenting and parent–adolescent sexual communication measures were used to assess the impact of intervention. Sexuality education program was presented for the parents of intervention group, in the form of four weekly 2-h sessions. Parents were assessed at the baseline, within one week post-intervention, and three-month follow-up to evaluate the outcome variables. The data were analyzed using the Chi -square test, two-sample t-test, general linear model analyses, and Bonferroni test. Results In terms of parent–adolescent general communication, parental monitoring, parent–adolescent communication about sex-related topics, parent’s sexual communication skills, parent’s self-efficacy, and responsiveness to sexual communication. There were no significant differences between intervention and control groups at the baseline (p>0.05). Compared to controls, intervention parents reported more improvement in general communication across the time; however, significant differences were not observed regarding general communication and parental monitoring (p=0.94, p=0.95). Parents in the intervention group significantly differed from those in the control group for the mean scores of parent–adolescent communication about sex-related topics (p=0.04), parent’s sexual communication skills (p=0.04), parent’s self-efficacy (p=0.002), and responsiveness (p<0.001) to sexual communication at each follow-up. Conclusions We identified the educational program as a promising tool for improving parent–adolescent communication regarding sexuality-related issues. This program provides the evidence for implementation of parent-based sexuality education programs.