Stark effect in hydrogen by an rotating electric field is discussed; the strength of the field does not change, however, its direction rotates around a fixed axis by a constant angular velocity. Schrodinger wave equation for an hydrogen atom is solved under such assumption that the external electric field causes only first order Stark effect. Wave functions are obtained for the ground state of the atom and the first excited state of it. It is shown that Lymann alpha line separates into seven components by the perturbation of the rotating field, although it does into three ones by that of a static field. In the case where the angular velocity of the field rotation is infinitely large, the effect of the perturbation vanishes so that the line consists of only one component.