Cancer is one of the most deadly diseases around the world. Oncolytic virus (OV) therapy is an anti-cancer approach based on using viruses to selectively target and kill cancerous cells and also their ability to stimulate antitumor immune responses. Vesicular stomatitis virus (VSV) has been investigated as a great platform for an oncolytic agent. Many modifications have been made to VSV to improve its oncolytic effects. One of such modifications by our lab is inserting Smac gene in the genome of VSV to generate armed VSV-S and VSV-Δ55S. The hypothesis is based on the fact that VSV infection triggers apoptosis through the intrinsic mitochondrial pathway, so overexpression of Smac via infection by armed VSV will reinforce apoptosis and increase the rate of cell killing. We conducted several experiments to examine effects of the inserted gene in viral replication and the enhancement in killing cancer cells compared to wild type VSV.