Fruit production is an activity of great importance in the Brazilian commercial balance and even more in the Northeastern region. Intermediation is a regular practice in the fruit exporting market due to existence of requirements, such as quality certificates, and of internal problems in production and commercialization, such as credit limitations and absence of product standardization. Large companies, cooperatives, associations and NGOs receive products from many small producers and export them together with their own products. In Northeast, it is common that the exporting agent offers contracts to producers that include technical, administrative and legal assistance plus input supply. This paper proposes a model, using the principal-agent approach of game theory, to the case of contracts between mango exporting agents and small producers, in Rio Grande do Norte. The contract type chosen by most of the producers is optimal for both parts and leads producers to apply a high level of effort in their production. However, in the long run, these contracts may be changed with strong impact on the small producers. Extensions of the model can include bargaining in the negotiations or temporal changes, moving from static to dynamic game cases.