Abstract: Influenza virus is the most important cause of annual morbidities and mortalities worldwide with numerous antigenic drifts and shifts. Inaccessibility to effective drugs and vaccines has made world health authorities to be interested in traditional medicine in order to prevent spread of the infectious agent. Garlic is one of the most famous of all plants in human history. It has been shown that garlic extract has various effects on different diseases.  The aim of this study was to evaluate garlic extract antiviral activity against influenza virus in cell culture. To study the potential antiviral activity, MDCK (Madin-Darbey Canin Kidney) cells were treated with effective minimal cytotoxic concentration of the extract and 100 TCID₅₀ (50% Tissue Culture Infectious Dose) of the virus during infection at different time periods. The viral titers were determined by hemagglutination (HA) and TCID₅₀ assays. The antiviral effect of the extract was studied at 1, 8 and 24 hours after treatment on the culture. To measure the amount of the viral genome synthesized at different times after treatment, RNA extraction, Reverse Transcription-Polymerase Chain Reaction (RT-PCR) and free band densitometry software were performed. Although the precise mechanism has not been defined yet, it was found that garlic extract with a good selectivity index (SI) has inhibitory effect on the virus penetration and proliferation in cell culture.