CdO thin film with different thickness and different particle size are prepared through radio frequency magnetron sputtering technique. Quantum confinement effect causes the significant changes in their optical properties showing significant changes in the optical band gap. The CdO films are very highly conducting and transparent. Transparent and conducting thin films of CdO with effectively increased optical band gap are very useful for different device applications like solar cell, optoelectronic devices. © 2011 World Scientific Publishing Company.