The interactions between oxalic acid (C2H2O4) and H2O on a polycrystalline Cu surface have been investigated by reflect ion-absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) methods. The desorption of H2O and C2H2O4 was studied; we found that the ice desorption temperature increases with the ice-film thickness. Desorption of the C2H2O4 layer involves a structural modification and sublimation. The H2O/C2H2O4 and C2H2O4/H2O interfaces and the codeposited C2H2O4+H2O were prepared on the Cu surface by varying deposition sequences of gaseous C2H2O4 and H2O at 155 K. We found that the interaction between ice and C2H2O4 does not lead to the H2O-induced deprotonation of C2H2O4 in a temperature range 155-283 K. However, H-bonding interactions between H2O and C2H2O4 can lead to the formation of a metastable oxalic acid-ice complex in the C2H2O4/H2O and C2H2O4+H2O systems during the TPD process. Desorption of H2O from the C2H2O4/H2O/Cu system is suggested to involve the diffusion of H2O through the top C2H2O4 layer. H2O desorption is followed by a rearrangement of C2H2O4 to form a C2H2O4 adlayer on Cu in the C2H2O4+H2O system. These experimental findings suggest that C(2)HlO(4) is not ionized oil snow and ice in the polar boundary layer and at upper tropospheric temperatures (similar to 240 K).