Particulate organic species contribute to the formation of cloud condensation nuclei and may play a role in the formation/growth of condensation nuclei. The field measurements in this paper investigated size distribution and mixing states of particulate oxalate (one of major organic compounds in aerosol particles) in the Arctic boundary layer in during the winter and spring. The variation of particulate oxalate concentration correlated well with nss-SO42- concentration. This correlation may be due to the direct emissions of oxalate and its precursors of oxalate from anthropogenic sources. The molar ratio of oxalate to nss-SO42- was found to gradually increase from winter to early spring with the recovery of solar radiation to the Arctic Circle. Individual aerosol particle analysis by means of laser microprobe mass spectrometry showed that most of the oxalate was internally mixed with sulfate in fine particle mode (0.2--2.0 ¿m).