The aim of this lecture is to present on Cosmic Microwave Background. 1960’s at scientists at Bell Laboratories detected background noise using a special “low noise” antenna. This static noise came from every direction and did not vary in intensity. The scientists soon realized they had discovered the cosmic microwave background radiation. The cosmic microwave background (CMB) is the thermal radiation left over from the time of recombination in Big Bang cosmology. here also briefly focus on origins of the CMB and differential microwave radiometer.