Thailand ranks fifth in the world production of mango after India, Pakistan, China and Mexico. But only one percent of its total production is exported, with largest export volume goes to Japan. The main preferential variety is Nam Dok Mai, occupying the Japanese market from 6.4 percent in 2002 to 32.9 percent in 2005. Majority of mango farmers in Thailand are independent growers. Export of quality mango is increasingly managed by farmers groups (FGs) to reduce transactional cost. This research project has general objective of developing mango cluster for improving competitiveness of mango in export market. Specifically it has three objectives, namely 1) to develop “mango cluster” processes for improving farmers’ capacity, 2) to analyze enabling conditions for developing “mango cluster”, and 3) to analyze opportunity for scaling out the “mango cluster” strategy. The participatory action research was conducted in collaboration with mango FGs in two provinces: Prao Mango FG (P-MFG) in Chiang Mai and Noen Mahpang Mango FG (NMP-MFG) in Phitsanulok. The key processes involved farmer meetings and workshops, farmer survey and individual household interviews, stakeholder workshops and field visits. Information from key informant discussion, field survey and farm household interviews were used as the basis for farmer workshops to provide interactive learning between farmers, and between farmers and researchers, and to help assess group performance. Various analytic tools were used in the farmers and stakeholder workshops, such as SWOT analysis, modified Porter’s Diamond Model, etc. The results showed that a series of farmer workshops to gain better understanding and trusts were essential step before multi-stakeholder processes were organized and conducted in developing mango cluster strategy. Farmers-researchers workshop to review on existing production technology and post harvest handling helped identify knowledge gap in proper chemical use and quality mango production. Tree pruning, floral induction, nutrient and pest management, and fruit wrapping were commonly practiced for quality mango production. However, fruit thinning was rarely done. The establishment of community learning center was recommended to provide better dialogue between farmers and researchers, and information service for farmers. The motivation of farmers joining group was to secure market and stable price, as well as to cut down transactional cost. The P-MFG, which produced late mango season lasting about one month, adopted diversified marketing strategy by contracting many potential exporters before harvest. This was to speed up the distribution. While the NPM-MFG mainly contracted with single fruit processing company prices over the four-month harvesting season with guaranteed price. The multi-stakeholder workshops involving private exporters, agro-chemical companies, major mango farmers groups from Chiang Mai, Phitsanulok, Phichit, and Phetchabun, staff of Offices of Agricultural Research and Development Region I (Chiang Mai) and II (Phitsanulok), Provincial Office of Agricultural Extension, National Science and Technology Development Agency (Northern Branch), and the Post Harvest Technology Institute, Chiang Mai University, etc. provided a compressive overview of supply chains from producers to overseas consumers. The improved logistics enabled the quality mango to be displayed for consumers in Japan and the Netherlands within 24 hours after farm delivery. This was enabling factor for supporting export potential. The multi-stakeholder workshops provided mutual understanding and improved communications between FGs and private sectors. Information on year-round production of mango from the established FGs in different regions was needed by the private exporters for marketing planning and operation. A central body, preferably universities, was recommended to coordinate and to foster the linkage between FGs, private exporters, and agro-chemical companies. It was recommended that multi-stakeholder processes were useful for developing “mango cluster”, supported by prepared information from different actors.