Online health information tools (OHITs) have been found to be effective in improving health outcomes. However, the effectiveness of these tools for older patients has been far from clear. This systematic literature review therefore provides an overview of online health information tool effectiveness for older patients using a two-dimensional framework of OHIT functions (i.e., providing information, enhancing information exchange, and promoting self-management) and outcomes (i.e., immediate, intermediate, and long-term outcomes). Comprehensive searches of the PubMed, EMBASE, and PsycINFO databases are conducted to identify eligible studies. Articles describing outcomes of patient-directed OHITs in which a mean sample or subgroup of age ≥65 years was used are included in the literature review. A best evidence synthesis analysis provides evidence that OHITs improve self-efficacy, blood pressure, hemoglobin levels, and cholesterol levels. Limited evidence is found in support of OHIT effects on knowledge, perceived social support, health service utilization, glycemic control, self-care adherence, exercise performance, endurance, and quality of life. OHITs seem promising tools to facilitate immediate, intermediate, and long-term outcomes in older patients by providing information, enhancing information exchange, and promoting self-management. However, future studies should evaluate the effectiveness of OHITs for older patients to achieve stronger levels of evidence.