An intake manifold for an engine includes a plurality of intake distribution pipes arranged in a side-by-side relation to one another; an intake inlet pipe provided in an end wall and arranged in a direction of the intake distribution pipes; a surge chamber provided inside the intake manifold, and providing communication between the intake inlet pipe and the intake distribution pipes; and an intake guide wall provided integrally with the intake manifold. The intake guide wall extending in the direction in which the intake distribution pipes are arranged. One surface of the intake guide wall is smooth-and-flat and the other side surface of the intake guide wall includes a plurality of thinned concave parts separated by a plurality of ribs provided between the concave parts.