The phase behavior after melting of crystalline-amorphous alternating lamella structure (CA-LAM) and cooling from disordered state in polybutadiene-block-poly(epsilon-caprolactone) (PB-b-PCL)/PB homopolymer blends was investigated using small-angle X-ray scattering (SAXS). As soon as CA-LAM disappeared by melting, coexistence of hexagonally packed cylinder (HEX) and layer structure was confirmed. On further increasing temperature, HEX transited to Gyroid (Gyr) and the layer structure still remained (the layer gradually disappeared or transited to HEX and Gyr at given temperatures). Under cooling process from disordered state, perforated layer (PL) structure first appeared and transformed into Gyr. Although the hysteresis of temperature dependence of domain spacing between heating and cooling process was observed, it was not observed any more when the sample was heated after aging for adequately long time. This hysteresis behavior was attributed to local distribution of PB homopolymer blended in block copolymer. When PCL chains crystallized, PB homopolymer was expelled out of PB domain. With the temperature increased and aging for a time, the PB homopolymer was redistributed into the PB domain and the equilibrium structures in this system were observed. (C) 2010 Elsevier Ltd. All rights reserved.