The evolution of the morphology of a crystalline/amorphous diblock copolymer poly(ethylene oxide-b-1,4 butadiene) (P(EO-b-BD)) upon crystallization in thin films was studied via interference optical microscopy. Two-dimensional crystallization confined within the PEO lamellar layers was observed with retention of the microphase-separated lamellar morphology formed in the melt state. The morphology was further characterized by TEM and electron diffraction which showed it to consist of alternating layers of PEO and PBD with PEO crystalline chains oriented perpendicular to the lamellar layers of the microphase-separated structure. Multiple parallel. layers of crystalline PEO were found by electron diffraction to be in orientational registry even though they were separated by approximately 10 nm thick layers of amorphous PBD.