A linearized theory is developed for obtaining the lift distribution on the wing with low aspect ratio. The theory is based on the assumption that, in the case of low aspect ratio wing, it is rather important to adopt not the projected surface into the plane of free stream but the wing surface itself as the lifting surface than to treat it from the non-linear theory. A linear approximation method useful in predicting the chordwise lift distribution on the rectangular wing with low aspect ratio is deduced from the present theory. The computed results from this approximation are compared with test data and show satisfactory agreement. From this fact, the propriety of the above mentioned assumption is proved. The lifting surface theory presented in this paper may be widely applicable in predicting the hydrodynamic forces on so kind of low aspect ratio wings, because of linearization of the theory.