PROBLEM TO BE SOLVED: To provide a cell culturing composition excellent in propagation efficiency of influenza virus.SOLUTION: A cell culturing composition includes MDCK cells enhanced in propagation efficiency of influenza virus by suppressing the expression and/or function of IRF7 or MAVS. The suppression of the expression of IRF7 is attained by introducing siRNA that is a double-stranded RNA composed of a sense strand of a base sequence represented by sequence number 1 and an antisense strand of a base sequence represented by sequence number 2. The suppression of the expression of MAVS is attained by introducing siRNA that is a double-stranded RNA composed of a sense strand of a base sequence represented by sequence number 5 and an antisense strand of a base sequence represented by sequence number 6.