We performed ultrasonic measurement on the rare-earth intermetallic compound PrInAg2 to examine the quadrupolar Kondo effect associated with the non-Kramers Gamma(3) doublet ground state. The characteristic softening of the elastic constant (c(11)-c(12))/2 below 10 K in PrInAg2 is attributed to the Curie term in quadrupolar susceptibility for the quadrupole O-2(2) = J(x)(2) - J(y)(2) of the stable Gamma(3) ground state. (c(11) - c(12))/2 turns to a slight increase with the - In T dependence below 0.1 K, which suggests the quenching of the quadrupolar moment in the quadrupolar Kondo state. Under applied magnetic fields of 10T and 15T above 8.7T corresponding to the Kondo temperature T-K of similar to 0.86 K, the behavior of (c(11) - c(12))/2 is described in terms of quadrupolar susceptibility for the stable 4f(2) state.