Consistent with Agenda 21 and the philosophy of ‘sufficiency economy’, Thailand has pursued sustainable agricultural development policy to complement its pursuit of sustainable national development. Primarily based on secondary information, this study first analyzes the evolving sustainable agricultural development policies, followed by an assessment of the achievements attained, where explanations are provided for the achievement or non-achievement. The findings reveal that Thailand began to pay attention to sustainable agricultural development policy starting in the early 1990s. However, it was only after the adoption of the philosophy of ‘sufficiency economy’ as the main sustainable development policy agendum that the country began to move seriously towards sustainable agriculture development. In this regard, several policy instruments were introduced, including crop diversification, reduced use of inorganic fertilizers and pesticides, and promotion of organic agriculture and healthy food. Overall, impressive achievements were made in introducing such policies, but those policies may have little effect on the ground, considering that conventional agriculture has still remained largely intact. The reasons for the divergence between the policies and actual practices are explained in this paper, while important policy relevant conclusions applicable to all developing countries are also deduced. Copyright © 2010 John Wiley & Sons, Ltd and ERP Environment.