Increase in bladder stiffness is associated with various pathological conditions. Measuring bladder viscoelasticity could be an important step towards understanding various disease processes and improving patient care. Here, we introduce Ultrasound Bladder Vibrometry (UBV), a novel method for rapid and noninvasive measurement of bladder wall viscoelasticity. UBV uses acoustic radiation force to excite Lamb waves in the bladder wall and track the motion using ultrasound pulse-echo techniques. Fourier space analysis of the tissue motion is used to calculate the Lamb wave velocity dispersion (change of phase velocity as a function of frequency). The measured phase velocity dispersion is fit with the antisymmetric Lamb wave model to estimate tissue elasticity and viscosity. Finite element analysis of viscoelastic plates was used to study the effect of curvature on Lamb wave dispersion. The feasibility of the UBV technique was demonstrated in ex vivo and in vivo settings.