The presence of oxygen isotopic anomaly in hydrogen peroxide (H2O2) has been established by measurements of three oxygen isotopes (O-16, O-17, O-18) in H2O2 from experiments on H2O2 formation using a water vapour discharge in presence of (O-2, CO2, Ar) gases and using VUV photolysis of water vapour. The termolecular OH recombination reaction may be account for the source of MIF in H2O2 due to a selective isotopic enrichment through the radical pair mechanism with non-equivalent nuclei. It was established that the magnitude of the observed MIF signals in H2O2 depended on the presence of oxidising gases. (C) 2018 Elsevier B.V. All rights reserved.