Evidence from correlational studies suggests outdoor recreation may enhance participants' environmental concern, but findings are inconclusive. Also, previous research has not systematically addressed the influence of interpretation services on environmental concern, and little research has been conducted in developing Eastern countries. Thus, this study's objective was to determine whether recreation participation (appreciative vs. consumptive forms) and/or interpretation programs (based on Tilden's principles of interpretation) influence Thai park visitors' environmental concern (EC) EC was operationalized through the measurement of three variables: specific environmental concern (SEC), worldwide environmental concern (WEC), and environmental behavior (EB). Data were collected through an experimental design. Two hundred forty Thai students were systematically assigned to one of eight experimental conditions defined by recreation type (appreciative vs. consumptive), recreation activity nested within recreation type (nature photography, hiking, motorcycling, and motorboating), and Tildenian interpretation (interpretation service provided vs. not provided). Results suggest that appreciative recreation activities enhance environmental concern, and interpretation can mitigate effects of consumptive forms of recreation, particularly in terms of worldview environmental concern and environmental behavior. Future research should assess a relationship between recreation specialization and environmental concern and the impact of recreation participant and/or interpretation services on participants' delightedness.