Porous microspheres of polyester±polyether block copolymer based on polycaprolactone/ polylactide/poly(ethylene oxide) (PCEL) were prepared by an emulsi®cation±solvent evaporation technique. The effect of hydrophilicity/hydrophobicity of the polymer on the morphology of the PCEL microspheres was studied and compared with that of polycaprolactone (PCL) and polycaprolactone/ poly(ethylene oxide) block copolymer (PCE) microspheres. It was demonstrated by X-ray photoelectron spectroscopy (XPS) that the enrichment of PEO segments on the surface of the microspheres occurred during solvent evaporation of the microdrops and lead to porous structure of the microspheres. The effects of the content and length of PEO segments of the PCEL polymer on the morphology of the microspheres were studied. The degradation behaviour of ®lm-like and microsphere-like PCEL was investigated at pH 7.4 and 37 AE 1 °C. The shape of the PCEL samples had no obvious effect on the degradation rate of the material and homogeneous degradation was a main process. The degradation rate of PCEL microspheres was enhanced in the presence of the enzyme lipase. 1 H NMR measurements revealed that the PEO content reduced with degradation time because the PEO segment was broken down and dissolved in the medium during degradation.