MP2 and M05-2x calculations with aug-cc-pVDZ basis sets were used to analyze intermolecular interactions in peroxyformic acid dimers. A total of 18 and 16 minima were located on the potential energy surface of HOOCHO dimer complexes at M05-2x and MP2 computational levels, respectively. The BSSE corrected interaction energies are in a range between 9 and 34 kJ mol(-1) at the MP2/aug-cc-pVDZ computational level. The atoms-in-molecules (AIM) theory was also applied to explain the nature of the complexes. The interaction energies have been partitioned with the natural energy decomposition analysis (NEDA) showing that the most important attractive term corresponds to the charge transfer.