A solid-phase-extraction ion chromatog. was developed for determining three residual impurities such as acetic acid (MCAA), dichloroacetic acid (DCAA) and chloride ion (Cl-) in crude oligonucleotide simultaneously.The final optimized conditions for testing were listed as follows by using Ionpac AS 23 (4 mm × 250 mm) anal. column, Ionpac AG23 (4 mm×50 mm) protective column, mobile phase as 0.8 mmol/L-1 NaHCO3 4.5 mmol/L-1 Na2CO3 and suppressed conductivity detector.The standard curve equations of MCAA, DCAA and Cl- were Y = 5.230 7X +0.014 (r = 0.999 7), Y = 19.162X -0.007 2 (r = 0.999 9), and Y = 507.4X -0.746 2 (r = 0.999 8), resp.MCAA, DCAA, and Cl- showed a good linearity in 0.002-0.400 μg/mL-1, 0.000 624-0.156 μg/mL-1, and 0.002 4-1.5 mg/mL-1, and detection limits were 0.02, 0.312 ng/mL-1, and 0.01 μg/mL-1, resp.The method is simple, fast, accuracy and can be used for impurities control of crude oligonucleotide.