To improve the luminescence properties of Sr2Si5N8:Eu2+ phosphor, Sr2-xYxSi5-xAlxN8:Eu2+ specimens in which Sr2+ and Si4+ were partially substituted with Y3+ and Al3+ were prepared by carbothermal reduction nitridation. The obtained Sr2-xYxSi5-xAlxN8:Eu2+ samples showed standard Sr2Si5N8 structure. The effects of Y3+ and Al3+ partial substitution on the structures and luminescence properties of the resulting specimens were investigated. Under excitation by near UV and blue radiation, Sr2Si5N8:Eu2+ exhibited a broad emission band at about 613 nm, originating from the 4f(6)5d(1) -> 4f(7) transition of Eu2+. As Eu2+ concentration increased, the emission peak positions red-shifted from 606 to 628 nm, occupying two different crystallographic sites labeled as Eu(Sr1) and Eu(Sr2). Also, incorporation of both Y3+ and Al3+ ions into Sr2Si5N8:Eu2+ significantly increased the luminescence intensity of Eu2+. This was attributed to modification of the crystal field environment of Eu2+. Overall, the improved luminescence intensities obtained through partial substitution of Sr2+ and Si4+ by Y3+ and Al3+, respectively, indicated the promise of Sr2-xYxSi5-xAlxN8:Eu2+ as red phosphor candidates in white light-emitting diodes at x = 0.16.