The melting of the semicrystalline poly(ethylene oxide)(PEO)/ poly(ε -caprolactone) (PCL) multiblock copolymer was investigated by small and wide angle x-ray scattering. The two-stage melting was found in which the PEO block and the PCL block melt independently. The crystalline PEO Bragg peaks disappear at 30.5 °C while the block spacing increases due to the chain relaxation. The PEO crystalline domain size decreases continuously in proportion to the amount of the crystalline part. Above 40 °C, the PCL lamellae domains started to melt and the integrated intensity of the PCL Bragg peak decreases with increasing temperature. In the case of the PCL, however, the crystal domain size decreases only slightly. This indicates that the number of the PCL crystalline domains decreases during the melting.