The long term trends in acid precipitation chemistry of Cryptomeria japonica stands and deciduous broad leaved forest dominated by Quercus serrata were monitored in the Sanbe University Forest from 1996 to 2001. The values of pH in rainfall and through-fall showed the range of 5.1-5.6. They were larger than that in stemflow of 3.7-3.9 in C. japonica stands. On the other hand, the pH in through-fall and stemflow in the deciduous broad-leaved forest showed higher range than in rainfall. The ion concentrations, <Ca>^<2+>, <Mg>^<2+>, K^+, <Na>^+ and <NO_3>^- were higher in deciduous broad-leaved forest than C. japonica stands. The <SO_4>^^^<2-> concentration showed a reverse trend between both forests. The values of pH in rainfall and through-fall changed seasonally, and showed low value, 4.5 in winter and high value, 6.0 in spring. That in stemflow showed the same change as through-fall, but the range was lower by more than 1.0 in C. japonica stands. The <Na>^+, <Cl>^-, <NO_3>- and <SO_4>^^^<2-> concentrations were high in winter and low in summer. These were influenced by the north-west wind of monsoon in winter.