Disclosed herein are a method for estimating acoustic velocity of an ultrasonic image and an ultrasonic diagnosis apparatus using the same. The method for estimating acoustic velocity of an ultrasonic image includes: (A) dividing each of the ultrasonic images into a plurality of blocks; (B) extracting contours of ultrasonic images for each block of one frame among the ultrasonic images; (C) calculating and analyzing average luminance values of each block; (D) determining the optimal block number using the average luminance values and selecting the optimal blocks; and (E) estimating and applying the real acoustic velocity, whereby the acoustic velocity is estimated in real time and is applied to the ultrasonic diagnosis apparatus.