The article aims to analyze, in the opinions that Dalmacio Vélez Sarsfield produced as an advisor to the State of Buenos Aires between 1854 and 1857, the conceptions around the rights to land, especially those referring to the notions of possession and property, and its articulation with the modernizing policy of the State of Buenos Aires. Far from finding defined dogmatic constructions, it will be noted their close relationship with the problems that affected the Buenos Aires campaign and that they received careful attention from historians who have focused on these issues: the advance of the border and the distribution of the new ones occupied lands, the situation of the emphyteuts, the preservation of the pan llevar lands, the installation of municipalities and the formation of ejidos, the performance of the Topographic Department, among others. For this purpose, Vélez’s arguments on Roman, Indian and national law and the reinterpretation of this regulation will be studied in the light of new liberal proprietary ideas. It will be noted that, like many contemporary jurists, Vélez did not manifest a rupturist position of the previous legal tradition, but rather that he conceptualized an exclusive property right that he linked with it.