Background <p>Postoperative cognitive dysfunction (POCD) is a common and serious complication among geriatric patients undergoing surgery for oromaxillofacial malignancies, significantly impedes rehabilitation and increases healthcare costs. Therefore, effective perioperative cognitive management is essential, yet it remains challenging. While mobile health (mHealth) applications offer potential solutions, their adoption among elderly populations remains low due to usability barriers.</p> Objective <p>This study aimed to develop and comprehensively evaluate a novel WeChat-based mHealth intervention, the WeChat Applet of Cognitive Dysfunction Assessment and Management (WACDAM), for the perioperative management of POCD in older adults undergoing surgery for oromaxillofacial malignancies, with a focus on its clinical effectiveness, usability, and implementation value .</p> Methods <p>This is a mixed-methods, participatory design study. This study employed a participatory design strategy to develop WACDAM in collaboration with geriatric patients, clinical specialists, and technical developers. Patients who underwent oral malignancy resection with neck dissection under general anesthesia between December 2020 and December 2021 were enrolled. POCD was assessed using the Z-score method, and risk factors were analyzed using multivariable logistic regression. Usability and user satisfaction were evaluated using the System Usability Scale (SUS), the user version of the Mobile Application Rating Scale (uMARS), and semi-structured interviews.</p> Results <p>Among the 112 elderly patients who underwent surgery for oromaxillofacial malignancy and completed both preoperative and postoperative (day 7) assessments, the incidence of POCD was 33.1% (37/112). Multivariable logistic regression identified older age (OR = 1.269, 95% CI: 1.056–1.525), lower education level (OR = 0.792, 95% CI: 0.644–0.974), hypertension (OR = 4.153, 95% CI: 1.355–12.732), sleep disorders (OR = 1.272, 95% CI: 1.001–1.617), prolonged anesthesia time (OR = 1.009, 95% CI: 1.001–1.018), and intraoperative hypotension (OR = 5.512, 95% CI: 1.240–24.506) as independent risk factors for POCD. The WACDAM performance evaluation demonstrated a SUS score of 70.17 and a mean objective quality score of 3.65 ± 1.03 on the uMARS, with the highest score in functionality (3.87 ± 0.98) and the lowest in engagement (3.48 ± 1.07). Subjective quality assessments (3.66 ± 1.06) corresponded closely with these objective metrics. In semi-structured interviews involving 20 patients and 10 clinicians, users reported that WACDAM significantly enhanced doctor-patient communication (mean satisfaction increase: 1.63 ± 1.32 points, <i>P</i> &lt; 0.01), improved the efficiency of POCD management, and was overall perceived as an acceptable and valuable clinical tool.</p> Conclusions <p>This study developed WACDAM, a pioneering WeChat-based mini-program for POCD management. Through a participatory design, the platform established an age-friendly interface and a dual-channel management system for both patients and clinicians, effectively reducing technological barriers for elderly users and facilitating early identification of high-risk POCD cases. This research provides a scalable, low-cost digital solution for perioperative cognitive management in elderly patients.</p>