Water-soluble ions are important constituents of PM_(2.5) and PM_(10),which play an important role in global climate change through their direct and indirect radiative forcing. A series of PM_(2.5) and PM_(10) samples were collected over the Yellow Sea and the Bohai Sea in summer 2013. The distributions and sources of the main water-soluble ions (Cl~-,NO_3~-,SO_4~(2-),Na~+,K~+,NH_4~+,Mg~(2+) and Ca~(2+)) and organic acid ions (CH_3SO_3~-(MSA),CH_3COO~- and HCOO~-) in the samples were analyzed by ion chromatography. The concentrations of the total water-soluble ions ranged from 21.16 to 25.07 mug/m~3 in PM_(2.5) and from 24.14 to 29.45 mug/m~3 in PM_(10),with the average values of (23.16 3.16) and (26.83 4.22) mug/m~3 respectively. The concentrations of the secondary ions (nss-SO_4~(2-),NO_3~-and NH_4~+) were extremely high,accounting for 90.65% and 79.87% of the total determined ions in PM_(2.5) and PM_(10),respectively. The calculated results of equivalent concentrations of anions and cations indicated that acid and alkaline compositions were neutralized completely. The ratio of nss- SO_4~(2-)/NO_3~-decreased greatly in recent years,due to the decrease of SO_2 from coal combustion. The average concentrations of MSA, CH_3COO~- and HCOO~- were (0.0062 0.0023) (0.0052 0.0024) and (0.0009 0.0003) mug/m~3 in PM_(2.5),and were (0.0083 0.0025) (0.0085 0.0024) and (0.0013 0.0005) mug/m~3 in PM_(10), respectively. In addition, the concentrations of MSA, CH_3COO~- and HCOO~- correlated well with NO_3~-in the samples, exhibiting the effect of human activities on the concentration changes of organic acid ions.