Embodiments for providing an elastic image are disclosed. In one embodiment, an ultrasound system comprises: an ultrasound data acquisition unit configured to transmit and receive ultrasound signals to and from a living body to output ultrasound data corresponding to a plurality of frames while applying compression to the living body; and a processing unit configured to extract frames from a (n−1)th frame to a (n−i)th frame on a basis of a nth frame, wherein n indicates an integer larger than one and i indicates a positive integer, detect an optimal frame for forming an elastic image among the extracted frames by using first displacement between the nth frame and each of the extracted frames based on the ultrasound data, calculate second displacement between the optimal frame and the nth frame based on the ultrasound data, and form the elastic image based on the second displacement.