222 Rn has been widely used as a tracer ofsubmarine groundwater discharge (SGD) processes because it offers certain advantages, such as being an inert gas that is found at high concentrations in groundwater. This studyshows, for the first time, the distribution of this element on the continental shelf adjacent to Rio Grande do Sul state, Brazil. It describes its relation with sources and oceanographic processes, as well as its contribution to the profile of SGD along the state coast that stretches over 400 km. Since it also aims to fill gaps in the understanding of the SGD process, it answers the following question: what are the constancy and the scope of the process along this coastal system? SGD quantificationwas made from 222 Rn mass balance. 222 Rn activity ranged from values below the detection limit to 1.23 ± 0.32 dpm.L -1 . Perpendicular to the coastline, 222 Rn activity decreased offshore at a rate of 0.5 dpm.L -1 .km -1 up to approximately 10 km from the coast, where it was constant and below 0.4 dpm.L -1 . Groundwater fluxes were 5.66 ± 1.30 (southern region), 2.06 ± 1.02 (central region), 5.50 ±1.50 (northern region) and 6.63 ± 1.03 cm.day -1 (northern region). Variability in advection rates found by this study shows that, incoastal systems which are dominated by a certain type of sediment, some factors, such as local hydrodynamics and geology, can alter SGD quantitatively.