Abstract: The present invention relates to an oncolytic virus and the use thereof, specifically, an oncolytic virus having suppressed thymidine kinase (TK) gene expression and comprising genes encoding granulocyte-macrophage colony-stimulating factor (GM-CSF) and a complement regulatory protein; and the use of such an oncolytic virus. The oncolytic virus of the present invention maintains its efficacy even when administered intravenously, and thus, it may also be applied to the treatment of various solid cancers and metastatic cancers in addition to superficial solid cancers. In addition, the oncolytic virus of the present invention acquires resistance to complement attack by expressing a complement regulatory protein on the surface of the virus, and thus, it is stable in the blood, and it maintains stable oncolytic activity when intravenous injection, and thus, it may reduce effective viral dosage to minimize the side effects of anti-cancer drugs.