A novel reddish-orange emitting phosphor Eu-activated KLaSiO4 was synthesized by the conventional solid-state reaction at 1200 °C. The luminescence properties of KLaSiO4:Eu phosphor were investigated, and the critical concentration of the activator ion (Eu3+) was established as 0.02 mol per formula unit. Chromaticity coordinates of a typical KLa0.98SiO4:0.02Eu phosphor were x = 0.614 and y = 0.385. The phosphor exhibited reddish-orange luminescence with dominating emission at 612 nm, corresponding to 5D0 → 7F2 of Eu3+. Furthermore, the phosphor was characterized by excellent thermal stability, implying its potential use in white light emitting diodes.