Hydrogen peroxide reacts with [MoO2Cl2(dmso)2] to produce orange crystals of the title complex, [MoO(O2)Cl2(dmso)2]. The structure is orthorhombic with distorted pentagonal bipyramidal geometry around the molybdenum ion. A short O‐O bond length suggested the presence of a superoxide, but electron paramagnetic resonance measurements definitely supported the peroxo structure.