Background Human papillomavirus (HPV) poses a significant public health concern, as it is linked to various serious health conditions such as cancer and genital warts. Despite the vaccine’s safety, efficacy, and availability through national school programs, HPV vaccination rates remain low in Israel, particularly within the ultra-Orthodox community due to religious and cultural barriers. Decision aids have shown promise in facilitating shared decision making and promoting informed choices in health care. This study aimed to assess the impact of a novel Web-based decision aid on HPV vaccination intentions, knowledge, decision self-efficacy, and decisional conflict among Israeli parents and young adults, with a specific focus on exploring differences between religious groups. Methods Two Web-based decision aids were developed for parents of children aged 10 to 17 y ( n = 120) and young adults aged 18 to 26 y ( n = 160). A quasi-experimental study was conducted among Hebrew-speaking parents and young adults eligible for HPV vaccination. Participants completed pre- and postintervention questionnaires assessing vaccination intentions, knowledge about HPV, decision self-efficacy, and decisional conflict. Results The decision aid significantly improved intentions toward HPV vaccination among most religious groups, except the Jewish ultra-Orthodox community. Ultra-Orthodox participants exhibited reluctance to vaccinate themselves or their children (odds ratio [OR] = 0.23, P < 0.001 for parents’ group; OR = 0.43, P < 0.001 for young adults’ group). Parental preference for vaccinating girls over boys (OR = 2.66, P < 0.001) and increased inclination for vaccination among Muslim-Arabs were observed (OR = 3.12, P < 0.001). Knowledge levels improved among ultra-Orthodox participants but not decisional conflict and self-efficacy. Conclusions The Web-based decision aid positively influenced the quality of HPV vaccination decision making among various religious groups in Israel, except for the ultra-Orthodox community. Culturally tailored approaches that address specific community concerns are essential for informed decision making. Highlights Human papillomavirus (HPV) vaccination rates in Israel are substantially lower than those of other routine vaccinations, particularly among religious and ultra-Orthodox communities, largely due to sociocultural beliefs and misinformation. A newly developed Web-based decision aid was implemented in a study involving parents and young adults to evaluate its impact on vaccination intent, knowledge about HPV, decision self-efficacy, and decisional conflict. While the decision aid significantly enhanced vaccination intention, knowledge, and perceived behavioral control among various religious groups, it did not yield the same outcomes within the ultra-Orthodox Jewish community. This study highlights the vital role of cultural adaptation in HPV vaccine decision aids within Israel, revealing significant disparities in vaccination perceptions and decisions among diverse religious and cultural groups.