Taiwan is highly active tectonically and intensively faulted resulting in occurrence of number of big earthquakes in the region. In the northern part of Taiwan Island, a group of volcanoes are distributed. These volcanoes are known as the Tatun volcano group (TVG). During the past decade, volcanological, seismological, and geochemical observations have shown that Tatun Volcano Group has potential for future eruptive activity. In the present study solid state nuclear track detectors (SSNTDs) technique has been used for the measurement of radon-thoron concentrations in soil gas for volcanic and seismic study in Taiwan. The semiautomatic track count using a Nikon digital camera coupled to a PC and employing software “SCION” has been checked and tested by comparing the results with manual counting. In order to study radon-thoron in volcanic areas, pre-calibrated radon-thoron discriminators with LR films has been installed in Hsiaoyoukeng (SYK), Dayoukeng (DYK), Bayen (BY), and Gungtzeping (GTP) of Tatun Volcanic area in a hole (about 50 cm depths) having different temperatures for a defined period (bi-weekly to monthly). Radon behaviour observed is different at above said sites. We have also monitor radon using SSNTDs along with active detectors (RAD 7) in Bayen (BY) area of Tatun for comparative study. The observations have shown potential precursory signals for some earthquakes that occurred during the observation period having an epicenter in and around the TVG. Our monitoring stations in TVG area are sensitive to the events within a distance of 60 km.