In the present report, bare CdO and CdO/MnO2 core/shell nanostructures of various cores and different shell sizes were synthesized using co-precipitation method. The phase, size, shape and structural details of the bare CdO and CdO/MnO2 nanostructures were investigated by X-ray diffraction, transmission electron microscopy (TEM), and Raman spectroscopy measurements. TEM micrographs confirm the formation of core/shell nanostructures. The presence of CdO (core) and MnO2 (shell) crystal phases was determined by analyzing the Raman data of bare CdO and CdO/MnO2 core/shell nanostructures. The Raman spectra of bare CdO nanostructures contain one broad intense convoluted envelop of three bands in the spectral range of 200–500 cm−1 and a weaker band located at ~940 cm−1. The intensity of these two Raman bands is decreased with the increase of shell size and disappeared completely for the shell size 5.3 ± 1 nm. Further, two new Raman bands appeared at ~451 and ~665 cm−1 for the shell size 1.3 ± 0.1 nm. These two Raman bands are assigned to the deformation of Mn–O–Mn and Mn–O stretching modes of MnO2. The intensity of these two Raman bands is enhanced with the increase of shell size and attains a maximum value for the shell size 5.3 ± 1 nm. The disappearance of characteristics Raman bands of CdO phase and the appearance of characteristics Raman bands corresponding to MnO2 phase for nanostructures of shell size 5.3 ± 1 nm authenticate the presence of CdO as core and MnO2 as shell in the core/shell nanostructures. Copyright © 2014 John Wiley & Sons, Ltd.