Embodiments for processing a color Doppler mode image in an ultrasound system are disclosed. In one embodiment, the ultrasound system includes: a Doppler signal acquisition unit configured to transmit and receive ultrasound signals to and from a target object to acquire first Doppler signals; and a processing unit configured to form color Doppler mode images including power images and velocity images and a mask for detecting a region of interest by using the color Doppler mode images, the processing unit being further configured to mask the power images and the velocity image by using the mask.