This study derives a fair allocation of economic margin resulting from brand unification of watermelon originated in Jincheon County in Chungbuk Province. A concept of Shapley value, a part of co-operative game, is used to derive the allocation ratio between two participants(Deoksan and Saengajincheon), where the shapely value is calculated according to the marginal contribution of each brand to the value of unified brand. One hundred thirty three farmers(sixty even from Deoksan and sixty six from Saengajincheon) were surveyed with the items of farmer's preference to brand unification, the expected price of watermelon with unified brand, and the need of criterion for the allocation of economic margin resulting from brand unification. Results show that the fair allocation ratio of economic margin are fifty five percent for Deoksan and forty five percent for Saengajincheon. A sensitivity analysis was performed to check the variation of the fair ratio by changing the expected price of watermelon with unified brand. The ratio with fifty five percent for Deoksan and forty five percent for Saengajincheon was robust in spite of price change.