The morphology of poly(styrene-ethylene/butylene-styrene) (SEBS) triblock copolymer films cast from the solution in xylene at different temperatures was investigated by transmission electron microscope. The SEES solution was first heated to a certain temperature, which ranges from 20 to 140 degreesC and then cast onto the surface of phosphoric acid at the same temperature to prepare specimen films. Three different kinds of morphologies including coexistence of a large number of branched cylinders and a small number of spheres, coexistence of cylinder region and near homogenous region, and coexistence of non-branched cylinders and spheres were observed corresponding to 20, 80-110, and 130-140 degreesC temperature zones, respectively. Moreover, it was found that the diameter of cylinders increases with the casting temperature. All these show an obvious casting temperature dependence of the microphase separation phenomenon.