This paper aims to monetarily value the cost of areas impacted by deforestation in the municipality of Rorainópolis located in the south of the State of Roraima/Brazil. The method used for this purpose is the Opportunity Cost, given its usefulness to estimate the income sacrificed in terms of economic activities restricted by environmental protection activities, or in unused deforested areas. The opportunity cost was considered to be the areas that are in disuse, i.e. areas that are being deforested, without, however, reflecting a use of agricultural production. The calculation used in this work considered that the annual opportunity cost of deforestation in the municipality was R$ 31,073,415 million, which shows a signalling for investments that encourage production in disused areas.