Background As the aging population is increasing significantly, the communication skills training (CST) on transitional care (TC) is insufficient. Aims This study aimed to test the effectiveness of an intervention (the online TC CST [OTCCST] and TC) through the perspectives of healthcare providers (HCPs), older patients, and family members. Methods A total of 38 HCPs caring for older patients were randomized to the experimental ( n = 18) or control groups ( n = 20), and 84 pairs of patients and family members were enrolled (experimental: n = 42 vs. control: n = 42). The primary outcome was HCP communication confidence; while secondary outcomes included patient quality of life (QoL), activities of daily living (ADL), rehospitalization counts, and family caregiving burden. Data were collected from HCPs using a scale measuring confidence in communicating with patients. Patient outcomes were assessed using the McGill QoL Questionnaire-Revised and Barthel Index. Family members were assessed with the Caregiver Burden Inventory. Rehospitalization counts were tracked for 3 months post-discharge. Data were analyzed using multiple regression analysis. Results Experimental group HCPs showed a significant improvement in communication confidence over the control group ( p = 0.0006). Furthermore, experimental group patients had significantly fewer rehospitalization counts within 3-month post-discharge ( p < 0.05). However, no significant group differences were found in patient QoL and ADL nor in family caregiver burden. Conclusion The OTCCST can effectively improve HCP communication confidence, and the combination of OTCCST and TC can reduce rehospitalization counts for older patients. The OTCCST allows HCPs to learn asynchronously at their convenience, ideal for continuing education, especially during the COVID-19 pandemic. Supplementary Information The online version contains supplementary material available at 10.1007/s40520-022-02251-4.