Blue phases (BPs) possess optical stop bands in a visible range because they have a three-dimensional cubic structure with lattice periods of several 100 nm. Furthermore, since the diffracted wavelength of BPs can be shifted by external electric fields, BPs are expected to be applied for tunable photonic crystals. However, the narrow temperature range about 1 <SUP>o</SUP>C has been a problem for BPs without polymer. In this study, we investigated the effects of doping with a dendritic molecule on the temperature ranges and the photonic band in BPs. In addition, we discuss a physical mechanism of the expanded temperature range in terms of the host liquid crystals.