The present invention is a block copolymer composition comprising an aromatic vinyl-isoprene-aromatic vinyl triblock copolymer (A) and an aromatic vinyl-isoprene diblock copolymer (B), (i) a ratio (MwDa/MwDb) of a weight average molecular weight MwDa of a polyisoprene block in the triblock copolymer (A) to a weight average molecular weight MwDb of a polyisoprene block in the diblock copolymer (B) being 0.5 or more to less than 1, (ii) a ratio of an aromatic vinyl monomer unit in all polymer components of the block copolymer composition being 10 to 30 mass %, and (iii) the block copolymer composition having a breaking strength of less than 8 MPa and an elongation at break of less than 1,100%; a pressure-sensitive adhesive composition comprising the block copolymer composition and a tackifying resin; and a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer that comprises the pressure-sensitive adhesive composition.