Acoustic imaging sonar DIDSON is very useful for observation of creature and inspection of objects underwater, which gives near optical video quality images. As the beam width is 28.8°in the horizontal and 12°in elevation, it is proved difficult to image the whole picture of survey. In this study we have developed several softwares for observing underwater creature using image-mosaicing and image-processing to overcome the above weakness. The experimental results on real images show the effectiveness of the proposed method.