The assessment for possibility of applying the carbon credit trading based on the clean development mechanism (CDM) into the reforestation of Huay Sai Royal Development study center has been conducted. The assessment shows that the forest area has been increased since a reforestation project started in 1989. The current denuded forest in the area is about 2,020.21 rai (3.2 square kilometers). However, upon studying the scenario of having or not having the CDM project, there is no significant different in the carbon storage of both scenarios. Therefore, CDM does not have additionallity. On the other hand, the return of investment study shows that the return was much less than the investment; yearly return of 29,495 USD compared with the initial investment of 130,000 USD. The study concludes that the reforestation does not fit with the CDM criteria and the investment will give less benefit in return. Therefore, the priority to apply the CDM to the area is low.