Introduction Health literacy is an important competency to make informed, shared decisions in line with patient’s preferences. On the other hand, lower health literacy is associated with poorer health outcomes. Evidence-based patient decision aids (EbPDA) are validated instruments to support informed medical decisions and empower patients for relevant involvement in their care. This study aimed to investigate the effect of a digital EbPDA for hypertension on health literacy. Methods In a randomized controlled trial, 124 participants were presented with a web-based scenario related to a newly diagnosed condition of arterial hypertension. The intervention group was provided with an online decision aid, while the control group was prompted to search for related information without support. Specific health literacy for hypertension was operationalized based on the European survey for health literacy (HLS-EU-Q47). Results The intervention group showed a statistically significant increase in subjectively perceived overall specific health literacy regarding hypertension (p=0.02, Cohen’s d=0.44). The effect was also statistically significant for the subcategories understanding, appraising, and applying health-related information (all p<0.05). At least equal results could be shown for participants with a lower level of education compared to participants with a high level. Conclusion The findings suggest that digital EbPDAs can be an effective and easily scalable instrument to improve populations’ specific health literacy. A possible advantage of the measure could be that patients are addressed concerning important and pressing personal decisions, fostering awareness of the individual’s need for health literacy to reflect one’s options and preferences. EbPDAs may also be a promising approach to target vulnerable populations, as the investigated EbPDA seems to perform equally in less versus more educated individuals. For future research, it may be interesting to investigate whether EbPDAs have effects on general health literacy that go beyond the disease specifically addressed.