Two kinds of multiblok poly (ether-ester) copolymers with different properties have been synthesized. One of them consisted of poly (ethylene terephthalate) as hard segment and poly-(ethylene glycol) (PEGT)

as hydrophilic soft segment while

another consisted of poly(ethy-lene terephthalate) as hard segment and poly (tetramethylene glycol) (PTMGT) as soft segment

which is a relatively hydrophobic one.Relationship between the microstructure and blood ooknpatibility has been observed by changing the composition of blends.M icrophase separated structure of blends has been determi-ned by means of VES.DSC

SEM and TEM. Blood compatiobility of the blends was evaluated by column beads method. The experimental results indicate that microphase separated structure and hydrophilic-hydrophobic balance of materials are important factors which affect the compa-tibility of these materials with blood.