Agriculture used to be an engine of economic growth in Thailand. Before 1980, an expansion of agricultural land increased outputs of the economy. Thai agricultural sector became a major comparative advantage in the international trade. In addition, as being the labor-abundant country, agriculture supplied an industrial sector with cheap labors and other factors of production. The role of agriculture in growth was undeniable. However, in 1980s, land surplus began to disappear (Siamwalla, 1996). Industry and service then stepped up to the frontier instead. That’s why agricultural value-added share to GDP becomes small as an industrial sector became a bigger sector as shown in figure 1.