ZnxMg1-xS : Mn thin film electroluminescent (TFEL) devices have been developed in a wide range of compositions, x between 0.16 and 1.0, for use as yellow/green-light-emitting displays. Electroluminescence shows the blue shift alike photoluminescence with the increase in Mg composition. The Zn0.98Mg0.02S : Mn TFEL device driven at 1 kHz has a high luminance of 1056 cd/m(2) and an efficiency of 1.21 m/W. The CIE color coordinates varied from (x,y) = (0.54, 0.45) at x = 0.98 to (0.47, 0.52) at x = 0.16 with the decrease in Zn composition x in consistence with the peak shift from 585 to 565 nm.