Informal caregivers are playing a major role in helping elderly people with their activities in daily life. The purpose of this work is to develop an Online Support System for Elderly Care (OSSEC) to provide services for informal caregivers in Thailand. The system has six modules which are: patient and caregiver profile manager, elderly care recommender applying case-based reasoning, daily care plan manager, elderly care activity notifier, elderly care information resource locator and caregivers’ social interaction platform. We have established the utility of OSSEC in enhancing the knowledge and ability of informal caregivers and in reducing their stress. In particular, we measured quantitatively the usefulness of OSSEC and evaluated user satisfaction as well.