A modified block copolymer composition comprising (1) 100 parts by weight of a modified block copolymer consisting of vinyl aromatic hydrocarbons and conjugated dienes, containing a functional group having at least one group selected from the group consisting of a hydroxide group, an epoxy group, an amino group, a silanol group and an alkoxysilane group, or a hydrogenation product of the copolymer, and (2) 0.5 to 50 parts by weight at least one of fillers selected from the group consisting of silica-based inorganic fillers, metal oxides and metal hydroxides is disclosed. This modified block copolymer composition is excellent in heat resistance, mechanical strength, transparency, abrasion resistance, and processability.