There are disclosed embodiments for forming an enhanced elastic image in an ultrasound system. An elastic image of a target object may be formed by scanning N scan lines. A control unit divides the N scan lines into M scan lines groups by using an acquisition period necessary for transmitting and receiving ultrasound signals to acquire ultrasound data. An ultrasound data acquiring unit transmits ultrasound signals to a target object and receives the ultrasound signals reflected from the target object at a predetermined transmission/reception sequence for each of the M scan line groups. This forms ultrasound data corresponding to each of the M scan line groups while a pressure is applied to the target object. An elastic image forming unit forms at least one sub elastic image corresponding to each of the M scan line groups based on the ultrasound data. The elastic forming unit sums M sub elastic images corresponding to the respective M scan line groups to thereby form an elastic image of the target object.