The central theme of the thesis is gestational surrogacy contract. Theanalysis is bounded to the effects arising from the consideration of its object, whether lawful or unlawful according to the rules of constitutional and civil lawof the Brazilian legal system. The theoretical framework is outlined by the works of Francisco Cavalcanti Pontes de Miranda - especially the notions about the legal business plans - and Marcel Mauss - specifically the Essay on the gift - and the school of Constitutional Civil Law - from which it has built an analysis of categories that permeate the whole study: human dignity, personal autonomy and dichotomy between thing and person. The overall objective was to investigate whether the object gestational surrogacy contract would support the concept of legality according to the legal system and constitutional principles. As a result, three specific objectives were outlined. The first conceptually delimited the terms object, legality and illegality in doctrine and Brazilian jurisprudence and found that these concepts carry content that must be appropriate in order to support this new contract category - which incorporates patrimonial and non patrimonial rights. The second, while investigating whether such agreements are taken into account by the Judiciary, it was found an affirmative answer. However, it exposed that the analysis made by the judiciary is limited to the recognition of legitimate filiation. The third specific objective identified that the judiciary has considered the object of gestational surrogacy agreement as lawful contract because it is based on guidelines established by Resolution n. 2.121/2015 of Federal Council of Medicine about the altruistic surrogacy. On the factual situation, there was noted the relativism of concepts delimited by the legal rule in order to be put into perspective of delicate cases. No further consideration about the legality of contractual object could be established before the analysed cases.