A light source module includes a housing receiving a light source. The housing includes a transparent light emitting plate with a micro structure positioned on an outer surface thereof. The micro structure includes a number of first and second light guide projectors. The first light guide projectors are positioned at a middle part of the outer surface, the second light guide projectors are positioned at two end parts of the outer surface. The first and second light guide projectors extend along the outer surface and are perpendicular to each other, cross-sectional surfaces of the first light guide projectors perpendicular to the extending direction of the first light guide projectors are semi-circular-shaped, and cross-sectional surfaces of the second light guide projectors perpendicular to the extending direction of the second light guide projectors are triangular-shaped. An illuminating device including the light source module is also provided.