The present study developed an assessment scale to measure the competitiveness of wellness destinations in Thailand, particularly from the perspective of the wellness tourism firm. A literature review and in-depth interviews informed the components and indicators for the assessment. Then, a scale was developed to evaluate the effectiveness and accuracy of the measurement scale using exploratory factor analysis and verification by confirmatory factor analysis. These analyses generated seven dimensions of wellness tourism: destination environment, travel and policy, infrastructure and capacity, manufactured and cultural resources, strategy and structure, novelty potential, and cooperative and proactive marketing. The results indicate strategies and considerations to improve the competitiveness of wellness destinations in Thailand. The assessment tool may be valuable for wellness tourism clusters and stakeholders to assess and promote wellness destination competitiveness.