Tritium and major ion concentrations in rain were analyzed in Kumamoto, Japan between 2001 and 2006 to examine present tritium concentration and seasonal variation. The average tritium concentration was 0.36 ± 0.19 Bq/L (n=104) and higher tritium concentrations were observed in spring than the other seasons. Among the ions, non-sea-salt (nss) SO42- showed higher concentration in winter while other ions did not show marked increase in winter. Based on the back-trajectory analyses of air masses, the increase in tritium concentrations in spring arises from downward movement of naturally produced tritium from stratosphere to troposphere, while the increase of the nss-SO42- concentrations in winter is due to long range transport of pollutants from China to Japan.