Synthesis of B-A-B type triblock copolymers of aliphatic polyester (PEs) and polystyrene (PSt) was investigated by using cyclic unsaturated PEs prepared by conventional polycondensation of 4-octene-1,8-diol and sebacoyl chloride. The obtained cyclic PEs underwent cross-metathesis with PSt containing a carbon-carbon double bond (C=C) at the central position, which was obtained by atom transfer radical polymerization (ATRP) of styrene with a bifunctional initiator containing a C=C bond. PSt with a longer methylene spacer between the C=C bond and PSt successfully afforded the PSt-b-PEs-b-PSt triblock copolymer. As another approach to obtain the triblock copolymer, cross-metathesis of cyclic PEs with 2-butene-1,4-diol or 4-octene-1,8-diol bis(2-bromoisobutyrylate)s was conducted to afford linear PEs having ATRP initiation sites at both ends, followed by ATRP of styrene. The unsaturated PEs segment in the triblock copolymer obtained by the second approach was converted into a saturated PEs segment by treatment with tosyl hydrazide and tributylamine. DSC analysis of the triblock copolymer containing the saturated PEs segment showed crystallinity when the PEs content was >= 14 mol %.