Abstract : In this paper, we propose a 3D mapping method by sensor fusion of two different sonars: a Forward looking (FLS) and a profiling sonars (PS). We utilize the complementary information of the sonars. FLS provides high quality horizontal information with high resolution, and PS provides reliable vertical information with medium resolution. To fuse the two sonar data, we used submap based line feature extraction method. To verify the proposed method, we conducted a tank test and seatrial.