Background <p>Rising healthcare demand and the high-intensity, unpredictable pacing of clinical work make it important to understand how healthcare workers sustain work engagement. Although work-life interface experiences have been linked to engagement, the role of work frustration, arising when staff encounter barriers while advancing their work, remains insufficiently clarified.</p> Methods <p>Grounded in Job Demands-Resources (JD-R) theory, this study examined the association between work–life balance and work engagement among healthcare workers and tested whether work frustration mediated this association. Data were collected via a questionnaire survey. Indirect effects were tested using regression models with bootstrapping.</p> Results <p>Work-life balance was positively associated with work engagement. Work frustration served as a significant mediator, with the indirect effect accounting for 60.61% of the total effect. The model explained 38.5% of the variance in work engagement.</p> Conclusions <p>These findings extend JD-R-based explanations of engagement differences in high-demand healthcare contexts by highlighting work frustration as a key pathway linking work–life balance to engagement. Practically, hospitals may support work engagement by improving work arrangements and work-life coordination, while also reducing recurring process barriers and repetitive rework that accumulate work frustration.</p>