We have calculated the structure of the complex between H2O and HOCO. The H2O-HOCO complex has a relatively large binding energy of 7.1 kcal mol(-1) at the B3LYP/6-311+S(3df,3pd) level of theory. Structure and vibrational frequencies were also calculated. Infrared spectroscopy is a possible method for detection of this complex due to the large shifts in frequency and intensities relative to the parent monomers of fundamental modes in the complex. These data are used to calculate equilibrium constant for the formation of the complex, as well as rate constants for its dissociation. These data suggest the formation of the H2O-HOCO complex may compete with HOCO dissociation in the OH + CO reaction in the presence of water.