Temperature range of cholesteric blue phase (BP) was expanded by infiltrating liquid crystal (LC) that exhibits blue phases into mixed cellulose ester membrane (MCEM). The expansion of the BP temperature range was induced by pinning effect on the network surfaces of membrane. In particular, the temperature range of BP I in the LC/MCEM composite is four times wider than that of pure BP LC compound. Solvent treatment of MCEM with aqueous solution of ethanol leads thinner network of MCEM and bigger expansion of BP I temperature range. Polarizing microscopic observations and reflection spectrum measurements of the expanded BP have been carried out. Cooling rate dependence of the BP temperature range was also investigated, which indicated that the expansion of the BP temperature range upon infiltrating LC into MCEM was induced by the pinning effect at network surfaces in the MCEM.