A facile, green, cost effective, and template or surfactant free strategy via a two-step route i.e. UV irradiation followed by dissolution-growth for the controlled synthesis of Mn-Co composite nanorings at room temperature was proposed. The nanorings structures and the process were systematically studied via TEM, HRTEM, EDX and XRD. Bir-MnO2 nanosheets first formed through the direct photolysis of KMnO4 under UV light irradiation. This was followed by a dissolution-growth process via the dissolution of Bir-MnO2 nanosheets by the generated H+ from the redox reaction between the added Co(NO3)2 and residual KMnO4, as well as the accompanied formation of CoOOH, and Mn-Co composite nanorings. It was found that a balance between the dissolution and growth rate was needed. Suitable pH, KMnO4 presence and the starting nanosheets like Bir-MnO2 were the key factors for the formation of nanorings. The obtained Mn-Co nanorings/TiO2 showed enhanced efficiency for the catalytic oxidation of HCHO. Based on the above understandings, it is believed that the developed dissolution-growth method can be adopted for the designing and preparation of other Mn-Co composite nanostructures which can be further applied for environmental pollution remediation. Keywords: KMnO4 irradiation, Template free green synthesis, MnO2 nanoring, Co3O4, Structural characterization