BackgroundImproving older people’s health-promoting lifestyle (HPL) may slow the progression of health conditions and improve quality of life. Electronic health (eHealth) literacy is increasingly important for individuals managing health in the digital age. Previous cross-sectional studies have shown a positive association between eHealth literacy and HPL among older adults. However, no longitudinal studies have examined the association over time, their temporal relationship, and the potential underlying mechanisms. ObjectivesTo examine the longitudinal association and temporal relationship between eHealth literacy and HPL among older adults, and to explore their underlying mechanism based on the Integrated Model of eHealth Use (iMeHU). MethodsThis longitudinal study was conducted among older adults in Jiangxi Province, China, from February to November 2022. Data were collected at baseline (T1) and 3-month (T2) and 6-month follow-up (T3), using online self-reported questionnaires. Older people’s eHealth literacy and HPL were measured using the Digital Health Literacy Instrument and Health-Promoting Lifestyle Profile-II. Statistical analyses included Linear mixed model (LMM), cross-lagged panel model (CLPM), longitudinal mediation analysis, and multi-group analysis. Results611 participants were included at T1; 464 (75.9%) completed the follow-ups at T2 and T3. The LMM results suggested that older individuals with higher eHealth literacy levels showed better HPL over time (adjusted β = 0.31, 95%CI: 0.27∼0.35, p<.001), after adjusting for covariates. CLPMs supported that eHealth literacy could predict older people’s improved HPL subsequently, but not the reverse. Attitude towards eHealth mediated the relationship from eHealth literacy to improved HPL, with a mediated proportion of 17.2%. In addition, the prospective relationships were stronger and only significant in older patients. ConclusionsFrom a longitudinal perspective, this study highlighted the important roles of eHealth literacy and attitude towards eHealth in improving older people’s HPL, especially for the patients. The findings provide robust evidence and practical implications to develop targeted interventions.