The small-angle neutron scattering investigation was carried out on semi-dilute aqueous solutions of block and gradient copolymers comprising pEOVE and pMOVE, pEOVE(300)-block-pMOVE(300) (Block). and p(EOVE-grad-MOVE)(600) (Grad). Here, pEOVE and pMOVE denote poly(2-ethoxyethyl vinyl ether) and poly(2-methoxyethyl vinyl ether), respectively, and the numbers indicate the degrees of polymerization. The monomer composition in the Grad had a gradient along the polymer chain. For 20.0 wt% solutions, a microphase-separated structure and physical gelation were observed both in Block and in Grad systems. In the case of the Grad system, a gradual microphase separation took place as a function of temperature via a micellization with a small radius of core, characterized by the "reel-in" process, i.e., a winding of polymer chains to the core of a micelle because of the gradient composition. On the other hand, the Block system underwent a stepwise transition with respect to temperature. The relationship between microphase separation and the theological behavior is explained from the viewpoint of microscopic structure. (c) 2006 Elsevier Ltd. All rights reserved.