A groundwater radon monitoring in the southern and western part of Sakhalin Island was carried out in 2014 in order to study the correlation between radon anomalies and the seismic activity of the region. The objects of investigations were located within large tectonic dislocations of the island—the southern part of the Central Sakhalin fault and the central part of the West Sakhalin fault. The soil gas monitoring was carried out using a Sirad probe (Quarta-Rad, Russia) and the continuous radon monitoring in the groundwater was carried out using a Radon Seismic Station (CPC-05, NTM-Zashita, Russia). The effect of geochemical parameters, namely, temperature, pressure and conductivity on the radon emission has been studied. The present work contains an analytical protocol which is based on the analysis of radon emitted from the fault planes, a geo- chemical precursor when predicting the tectonic activity.