When evaluating the effectiveness of the drug Mefloquine against SARS-Cov-2 coronavirus, in vitro experiments examined its toxicity for African green monkey kidney cell culture - Vero C1008, as well as antiviral activity against SARS-Cov-2, which was evaluated by suppressing the cytopathic effect the virus. A study of the toxicity of the drug Mefloquine showed that the concentration at which the drug exerts a cytopathic effect against 50% of Vero C1008 cells is 4.5 μg / ml. The maximum tolerated concentration (MTD) of Mefloquine is 2.25 μg / ml. A study of the effectiveness showed that 1 day after infection, the antiviral effect of Mefloquine was recorded when the drug was added 24 hours and 1 hour before infection with SARS-CoV-2, as well as when it was added 1 hour after infection, the cell culture was already at a concentration of 0.5 μg / ml Mefloquine at a concentration of 2 μg / ml, added to the Vero C1008 cell culture 1 hour after the introduction of SARS-CoV-2, completely blocked the action of the virus for 2 days after infection.