The syndiotactic polystyrene membranes containing the delta-form which is a clathrated crystal with some solvent molecules as a guest and so-called "complex", were prepared by casting from its toluene solution at 85degreesC and room temperature. In order to evaluate the thermal stability of the complex in the two membranes, WAXD and time-resolved FT-IR measurements at various temperatures were performed. WAXD profiles suggested that the content of the complex in the membrane cast at room temperature was higher than that in one cast at 85degreesC. The transformation from TTGG helical to TT planar conformation were observed for the both membranes, but only above 190degreesC for the membrane cast at room temperature, indicating the retention of the helical conformation at a wide range of temperature.