In a previous study, an immiscibility loop in the isotactic polypropylene/partially hydrogenated oligo(styrene-co-indene) (HSI) blend was found by the cloud point method. Then morphology development both at one phase region outside the loop and at two phases inside the loop was investigated. At temperatures studied, a non-linear growth of the spherulite was observed and it was ascribed to the rejected HSI at the growth front of the spherulite. At one phase region just outside the loop, crystallization preceded, and it induced liquid-liquid phase separation at the trapped region between spherulites. At two phases inside the loop, spinodal decomposition proceeded, the crystallization from the decomposed state followed, and then the crystallization induced the dissolution of the liquid-liquid phase separation at the growth front of the spherulite. This behaviour, phase change from the one phase to the two phases and from the two phases to the one phase, was interpreted by the rejected impurity (HSI) at the growth front during crystallization.