Formation of higher-order structure in crystallization from microphase-separated melts was studied for polystyrene-polyethylene (PS-PE) diblock copolymers and PS-PE-PS triblock copolymers with time-resolved synchrotron small-angle X-ray scattering (SR-SAXS) techniques. The PE block was crystallized at temperatures when the PS block was in the glassy state. In both crystallization and melting processes, only the peak intensity in the SR-SAXS curve changed, however, the peak positions including higher-order peaks did not change. This means that the microphase-structure in the crystalline state was completely the same as that in the molten state. These behaviors were observed regardless of any melt microphase structure. Also, once a stable microphase structure was formed in the molten state, the structure was not changed even if crystallization and melting were repeated. Behavior of crystallization from such microphase-separated melts was also studied. Apparent activation energies of crystallization were high for all block copolymers, compared with that for the PE homopolymer. In particular, the triblock copolymers showed higher apparent activation energies than the diblock copolymers. Both degrees of crystallinity and Avrami indices were greatly suppressed in crystallization from the cylindrical domain. (C) 2004 Wiley Periodicals, Inc.