Surface water quality of medium-small rivers in the plain river network region (PRNR) of North Jiangsu Province was primarily investigated,with Sheyang County and Xinghua County as the representative areas.Different forms of nitrogen and phosphorus and COD concentration in surface water were analyzed.Mean TN,TP and COD concentrations of surface water in Sheyang County were 2.091 mg · L-1,0.482 mg · L-1 and 29.90 mg· L-1.Meanwhile,those in Xinghua County were 1.635mg · L-1,0.100 mg · L-1and 8.480 mg · L-1 respectively.TN and TP concentrations in Sheyang County had exceeded Category V of national surface water quality standard ( GB3838-2002,2.0 mg · L-1 and 0.4 mg · L-1 for TN and TP).Dissolved forms of N and P in both sites took the main proportion in the surface water.About 60％ and 71％ of N and P were in the dissolved forms in Sheyang County,and about 81％ and 58％ of N and P were in the dissolved forms in Xinghua County.Nitrate ( NO3-N ) occupied the main form in the total dissolved nitrogen (TDN) for both sites,and dissolved reactive phosphorus (DRP) did also so in the total dissolved phosphorus (TDP).Less than 10％ of the dissolved N was in the forms of ammonium-N ( NH4-N) for both sites.The river network structure and the geographical background might partially explain the difference of surface water quality between two research sites.Compared with surface water in the PNRN of Taihu lake watershed of South Jiangsu Province,the water quality in the PNRN of North Jiangsu Province was still quite good,especially in terms of nitrogen concentration.While,phosphorus concentrations in Sheyang County had accumulated to a higher extent,which were almost equal to those in Taihu lake region.So,more attention should be paid to those areas where have already suffered from water pollution in North Jiangsu Province such as Sheyang county.