Three groups of Ge–As–S glasses with compositions of (I) Ge x As 40− x S 60 ( x = 25, 30, 35 at.%), (II) Ge x As 10 S 90− x ( x = 25, 30, 35 at.%) and (III) Ge 30 As x S 70− x ( x = 5, 10, 15 at.%) were studied to understand the role of glass composition in determining physical and acousto-optic properties. For each group of glasses, the glass transition temperature (T g ), micro-hardness (H v ), elastic modulus and acoustic velocity increased with the addition of Ge, and the elements that determine the magnitude of performance variation are Ge > As > S. All glass samples had optical transmission higher than 54% at 633 nm, and the level of sulfur content determined the value of the optical bandgap (E g ). The glass with the tightest network structure realized the lowest acoustic attenuation (α) of 1.49 dB/cm at 25 MHz ultrasonic frequency. Furthermore, the maximum refractive index (n = 2.482) in Ge 30 As 15 S 55 glass contributed to the maximum acousto-optic figure of merit (M 2 ) of 209.78 × 10 −18 s 3 /g at 633 nm, which is close to 130 times greater than that of fused quartz. • Ge-As-S glasses were proved to be excellent acousto-optic functional media at 633 nm. • Control variate method was used to study the role of elements in determining the performance changes. • 99~135 times M 2 were obtained from the glasses studied greater than that of fused quartz.