A method for producing a resin additive composition is a method for handling, as a solid, a compound that can maintain a liquid state or fluid state at 100° C. for 30 minutes or longer, and includes causing 100 parts by mass of a styrene-based elastomer (A) to be mixed with 50 to 250 parts by mass of a compound (B) that can maintain a liquid state or fluid state at 100° C. for 30 minutes or longer. A resin additive composition is obtained by mixing 100 parts by mass of a styrene-based elastomer (A) with 50 to 250 parts by mass of a compound (B) having a melting point of 100° C. or lower.