Changes in tissue mechanical (elasticity, viscosity, etc.) properties are often associated with tissue pathology. In this paper, we present an ultrasound method capable of imaging the shear viscosity of soft tissue. This method is based on the measurement of creep function where tissue viscosity can be assessed by measuring slowly varying residual mechanical deformations induced by steady external forces rapidly applied at the surface. A finite element analysis of internal deformations of inhomogeneous viscoelastic medium was performed to investigate the capabilities of viscosity imaging. Then the ultrasound measurements of creep function were performed in the tissue sample (bovine muscle) to remotely assess viscoelastic properties of the tissue. The results of numerical and experimental studies suggest that time-dependent deformations can be measured with ultrasound to estimate and image both tissue elasticity and viscosity.