Background: Older adults with a family cancer history (FCH) face an increased cancer risk, which may adversely impact their emotional well-being. Internet-based eHealth technologies (IETs) provide a potential solution to this challenge. This study examines the influence of using IETs on the emotional well-being of older adults with FCH. It also delves into the mediating pathways through health information self-efficacy and cancer fatalism. Methods: This study conducted a mediation analysis using data from the Health Information National Trends Survey (HINTS 6) collected from March 2022 to November 2022, focusing on older adults with FCH who had previously searched for cancer-related information (N = 1,280). Results: In the mediation model, no positive direct associations between IETs usage and emotional well-being were found. Only health information self-efficacy and cancer fatalism were found to mediate the relationship between IETs usage and emotional well-being serially (β = 0.007, 95% CI [0.003, 0.012]). Conclusions: The findings inform health information professionals and healthcare practitioners on enhancing the impact of IETs usage on individual health information self-efficacy, which mitigates cancer fatalism, contributing to better emotional well-being in the digital era.