An EPDM composition that includes 1 to 12 parts by weight of liquid polybutadiene and 1 to 12 parts by weight of a plant-derived component-containing terpene resin based on 100 parts by weight of a plant-derived component-containing ethylene-propylene-diene terpolymer. The EPDM composition is obtained by adding, to EPDM that has, at least in part, a plant-derived component with low environmental impact, liquid polybutadiene, which is compatible with EPDM and can improve roll processability by reducing the compound viscosity, and further using a specific amount of a plant-derived component-containing terpene resin for the biomass degree, which is reduced due to the addition of the liquid. The rate of change in biomass degree is less than 1.5% in comparison to a composition to which liquid polybutadiene and a plant-derived component-containing terpene resin are not added.