This work investigated the characteristics of acid precipitation collected in Taipei, Taiwan during 1991-1995 by performing cluster analysis. The extent to which meteorological conditions influence precipitation chemistry was also elucidated. Three potential sources of water-soluble ions in rainwater were identified: seasalt aerosols (Na+, Cl- and Mg2+), anthropogenic pollutants (H+ and NO3/-), and mixing sources associated with sulfate (nss-SO4/2-, NH4/+ and Ca2+). As the northeast flow prevailed during the northeast monsoon season, the concentrations of seasalt and sulfate ions in rainwater were significantly high. During that season, a typically high ratio of nss-SO4/2-/NO3/- was also observed, indicating that Taipei might receive foreign pollutants via a long-range transport. In contrast, when the Pacific high dominated the region, nitrate concentration in rainwater was significantly elevated. Also during that period, the ratio of uss-SO4/2-/NO3/- was substantially lower, indicating the prominence of acidic substances contributed by local sources.