In 2011, the released radioactive materials including tritium (T) from damaged reactors at Fukushima Dai-ichi nuclear power plant has caused much environmental problems. After the Fukushima Dai-ichi Nuclear Power Plant Accident, the specific activity of T in precipitation was increased in Niigata city. In this study, each monthly precipitation (imitative ground infiltrated precipitation) was collected at the rooftop of Niigata University. Such a sample was subsequently enriched by electrolytic enrichment method (SPE method), and the specific activity of T of each enriched sample was measured by low-background liquid scintillation counter. In addition, the relation between specific activity of T and nssCa2+ (i.e., non-sea-salt Ca2+) concentration in monthly precipitation was also discussed. Moreover, the concentrations of cations, i.e., Na+, K+, Ca2+, and Mg2+, in monthly precipitation and the specific activity of T in spring water at top of Mt. Zao (and other mountains in Fukushima prefecture) were also measured. Based on the above-mentioned matters, it was found that the influence of the Fukushima Dai-ichi Nuclear Power Plant Accident on environment in Niigata city almost disappeared after four months from the accident.