This study aims to examine a significant difference in performance of, and attitudes towards, environmental tourism among domestic tourism companies by their types and scale, and to propose a policy direction for a new certification program on environmental tourism. This study conducted a survey with 152 tourism accommodations and 150 travel agencies. As a result, this study found that tourism accommodations and a large scale of companies had participated in environmental management practices more often than travel agencies and a small scale of companies. Also, tourism accommodations were more likely to recognize well a relation between their business and environmental tourism, and were more likely to participate in a new certification program than travel agencies. A large scale of tourism accommodations showed more positive attitudes towards environmental tourism than a small scale of tourism accommodations. On the other hand, all of the travel agencies showed less positive attitudes towards environmental tourism regardless of their size. In conclusion, this study proposed that the government should adopt a different approach to a new certification program according to tourism companies` types and scale, also it should provide a variety of incentives and supports for tourism companies.