A current oscillation, observed for H2O2 reduction on atomically flat Pt(lll) electrodes in a potential region from about 0.22 to 0.05 V vs NHE, and previously called oscillation E, was enhanced much by adsorbed iodine atoms of a submonolayer amount, showing an extension of its potential region toward the positive. Besides, the iodine adsorption led to an appearance of oscillation E even for atomically flat Pt(100), for which no oscillation E appeared in the absence of adsorbed iodine. The results were explained on the basis of a previously proposed model for oscillation E, including autocatalytic effect of adsorbed OH on dissociative adsorption of H2O2 (the first step of H2O2 reduction). Mathematical simulation by addition of catalytic effect of adsorbed iodine atoms on the dissociative adsorption of H2O2 has reproduced the observed enhancement of oscillation E. It is shown that the concept of the catalytic effect of adsorbed iodine atoms has the same theoretical basis as the autocatalytic effect of adsorbed OH.