This paper deals with experimental and analytical analyses of fish pectoral fin motion and performance tests of apparatus of pectoral fin motion from viewpoint of maneuverability of underwater vehicles. Observation of pectoral fin motion of Black Bass revealed that the combination of feathering motion and lead-lag motion of a pair of pectoral fins generates the fish motion of advancing, backward swimming, hovering and turning. The apparatus making the feathering motion and the lead-lag motion of the pectoral fin generates thrust force in a certain range of phase difference between both motions. The unsteady vortex-lattice method including the effect of viscosity can express fairly well the unsteady forces acting on a pectoral fin model with feathering and lead-lag motions in a range of the phase difference between both motions where it exerts thrust force. The fish model consisting of fish body model and a pair of the apparatus of pectoral fin motion can not only swim forward and backward and turn in the same position, but also swim in the transverse direction.