The phase transformations and luminescent properties of Eu-doped Ca1-xSrxAl2O4 phosphors were investigated. Ca1-xSrxAl2O4:Eu2+ phosphors were synthesized by a solid-state reaction with a flux, H3BO3. A phase transformation from monoclinic CaAl2O4 to monoclinic SrAl2O4 was observed as the x values increased. A high-temperature hexagonal phase of SrAl2O4 was formed during this transformation as an intermediate phase under an H2 atmosphere due to oxygen vacancies; this did not occur in an air atmosphere. Accordingly, the emission spectra shifted from a blue region to a green region as x increased.