This is very unfortunate that even in 21st century most of us are still unaware of the fact that the microbial origin of cancer exists in nature. And, this is all due to the lack of knowledge about their potentialities in causing cancer in human and animals. Further, as in recent past, some of these viruses having high rate of mutabilities and adaptabilities have already been proven their abilities to transform the host cells dividing indefinitely. The present review discusses some of the oncogenic viruses developing human cancers including their mechanisms of cancer development known so far in the same field.