Localization under water is required for the underwater mobile robot to conduct the survey autonomously. There is a conventional method using inertial navigation system as a localization under water, however it takes high costs. In this study, we propose a laser odmetry as a localization for underwater mobile robot. The laser odometry is a method to estimate motion by tracking the laser speckle pattern. It can measure three dimensional positions and a rotation. In this paper, we introduce a principle of the laser odometry, the construction of the sensor unit, and the results of measurement accuracy experiments under water.