A series of europium Eu3+-doped orange-red emitting phosphors were synthesized through a high-temperature solid-phase reaction using NaSr4(BO3)3 as the host in an atmosphere of air. The effects of calcination temperature and the contents of boric acid and Eu3+ on the photoluminescent properties of the as-prepared phosphors were investigated. In particular, the addition of boric acid in excess of the stoichiometric ratio could significantly improve the single-phase purity of the host. Meanwhile, the synthesis times for the phosphors were also reduced. The crystal phases and fluorescent properties of NaSr4-x(BO3)3:xEu3+ were characterized using X-ray powder diffraction analysis and a fluorescence spectrophotometer, respectively. The luminescent intensity of the phosphor was highest at the calcination temperature of 880℃ for 3 h, which was the optimum condition for forming single-phase NaSr4(BO3)3 hosts. All prepared NaSr4(BO3)3 phosphors belonged to the cubic crystal system. The maximum excitation wavelength was 392 nm. The main emission peaks were observed at 591 nm (orange light) and 615 nm (red light), which corresponded to the 5D0→7F1 and 5D0→7F2 transitions of Eu3+, respectively. Furthermore, NaSr3.92(BO3)3:0.04Eu3+ reached the maximum intensity of the main emission peaks, and the red-emitting performance was outstanding. The ratio (R/O) of the intensities of the emission peaks of red and orange lights could be affected by changes in the contents of Eu3+, so as to enrich and simplify the strategies for improving the red-emitting light purity. This provides a basis for the development of high-brightness and high-color-purity red-emitting phosphors for LED chips excited by near-ultraviolet light.