This study sought to determine the factors influencing rice farmers’ adaptation to a slow-onset hazard such as saltwater inundation. The research is based on a survey conducted through personal interviews using Kobotool App consisting of 326 coastal rice farmers in Northern Mindanao, the Philippines and 258 rice farmers in two provinces in the Mekong Delta in Vietnam. There were four levels of analyses for the assessment of the feasibility of the adaptation measures implemented by the farmers. First, it classified adaptation measures into specific categories: technology based, farm-based crop management, ecosystem-based adaptation, off-farm income diversification, and other measures. Second, it developed a multi-criteria assessment tool on adaptation measures based on stakeholder analysis and expert judgment based on four major feasibility criteria. Third, it determined the level of adaptation based on the combination of measures and the feasibility of the chosen measures by constructing a measure-based adaptation index (MAI). Finally, it came up with a model showing the factors influencing the MAI of the farmers. The results revealed that adaptation takes place at different levels in the two countries based on the diversity of measures, the feasibility of the various measures, and the varying conditions of saltwater inundation. The empirical evidence provides systematic support for the hypothesis that adaptation measures are influenced by a confluence of social, institutional, and economic factors.