Tissue stiffness is generally known to be associated with pathologic changes. Ultrasound indentation is able to assess the mechanical properties of soft tissues. Conventional ultrasound indentation devices use rigid flat-ended transducers to directly contact with the tissues and typically operate in the frequency ranging between 2 M Hz and 10 MHz. This paper introduced a novel ultrasound indentation system using water jet compression. The water jet served as an indenter as well as a medium for the propagation of the ultrasound beam. High frequency focused transducer was used to measure the indentation deformation at a microscopic level. It has been demonstrated that the system could effectively assess the tissue-mimicking phantoms with different stiffness. Moreover, another advantage of this novel indentation system was to apply C-scan on soft tissues rapidly and conveniently. By applying different pressures on C-scan sequences, the modulus image of the tissue could be obtained. This paper presented the preliminary results on gel phantoms. The spatial resolution and the sensitivity of the measurements, the reproducibility of the results were also discussed ; Department of Health Technology and Informatics ; Refereed conference paper