This study examines 'what taxation form is applied to carbon credit operations in Brazil in companies that are developing projects in the context of the Clean Development Mechanism (CDM)'. The exploratory research applies a qualitative approach to answer this question. A questionnaire was sent to all Brazilian companies with CDM projects that received approval from the Inter-Ministerial Commission on Global Climate Change (CIMGC) without safeguards, according to the list of the Brazilian Ministry of Science and Technology. Out of 117 companies listed, only five answered the research instrument, which represents an accessibility sample. The results show that, as for the tax treatment applied in the companies under analysis, Income Tax for Legal Entities (IRPJ) and Social Contribution on Profits (CSLL) should be charged on carbon credit operations. However, there is no agreement about due taxes in the research sample, as no specific fiscal legislation exists on carbon credits in Brazil.