The present invention relates to a complex comprising a compound of formula (I), or a plant extract comprising the compound or a fraction thereof and stevioside, or a plant extract comprising the stevioside or a fraction thereof, and relates to a pharmaceutical composition for preventing or treating an influenza virus infection comprising the complex as an active ingredient. Also, the present invention relates to a food composition for preventing or improving an influenza virus infection, a virucidal quasi-drug composition, a virucidal feed additive, and a feed, which comprises the complex as an active ingredient. According to the present invention, the complex comprising a compound of formula (I), or a plant extract comprising the compound or a fraction thereof and stevioside, or a plant extract comprising the stevioside or a fraction thereof exhibits a virucidal effect and an effect of inhibiting cell degradation against an influenza virus as well as antiviral efficacy in a specific pathogen-free (SPF) chicken, and thus can be usefully used in the prevention and treatment of an influenza virus infection.
