A method for measurement of the bladder wall nonlinear elasticity is presented. The method is based on acoustoelasticity modeling of the bladder tissue modulus of elasticity changes at different volumetric loading levels. At each loading volume, tissue strain is obtained from the real-time images. Using acoustic radiation force, a transient Lamb wave is excited on the bladder wall and shear elasticity is obtained from 2-D Fourier analysis of tissue motion spatial-temporal dispersion maps. Experimental elasticity and strain data are then used to obtain nonlinear elasticity parameter, A, using non-linear least square optimization. The method was tested in 9 ex vivo porcine bladder samples before and after treatment with formalin. The estimated nonlinearity parameter, A, was significantly higher in the treated samples compared to intact (P < 0.0021).