Abstract Various kinds of robots have been developed actively with progress of computer, and the operations with robots in the extreme environment such as rescue, space and ocean are getting practical solutions. The underwater robots are expected as one of solutions for underwater activities, i.e., maintenance of underwater structures, observations, scientific research, and their efficiencies are investigated in the oceans during recent decades. And according with human activities, the underwater structures are also getting large-scale and large-depth. In order to do safe and efficient works, the underwater activities are desired to be carried out automatically as possible. This paper describes development of an autonomous underwater vehicle for observation of underwater environment.