In this paper, high density polyethylene (HDPE)/poly(ethylene-co-butene) (PEB) blend (50/50 wt%) was prepared through solution blending and then compression molding, and subsequently examined by laser scanning confocal microscopy (LSCM). The PEB used in this experiment was labeled with a small quantity of a fluorescein derivative to render fluorescence. The initial films showed uniform dye distribution and no indication of phase separation within the resolution of optical microscopy. Sample films annealing at 140℃ followed by rapid cooling to room temperature showed obvious phase separation and bicontinuous structure. The present work indicates that by labeling one component with fluorescein derivative, LSCM can efficiently perform in situ depth profiling of polymer blends.