New Rb/Sr whole rock isochron ages have been determined for the main lithological units that occur in São Paulo and Rio de Janeiro States. These rocks belong to the "Serra do Mar" domain. The purpose of mis work is to characterize the sequence of the geological events as well as the possible relationship between the different rocks. The geochronological data suggest that the paragneisses and the basement rocks, represented by orthogneiss nuclei, were generated under amphibolite conditions around 700 Ma. At the same time the leucogranites were generated by partial melting processes and injected into both gneiss types. Tarditectonic granitic magmatic activities took place within ductile shear zones. One of the granites, the Getulândia granite, yielded an age of 514 Ma, falling in the range of the late Brasiliano Cycle which extended into the Middle Cambrian.
