A light source module applicable to a projection device includes a heat dissipation assembly, a first light source, and a second light source. The heat dissipation assembly includes first and second heat dissipation components. The first heat dissipation component includes a first base and a first fin set. The first fin set has a first ventilation surface. The second heat dissipation component includes a second base and a second fin set. The second base has a first surface, a second surface and a ventilation opening. The first surface is opposite to the second surface. The second fin set is arranged on the first surface. The second surface faces the first ventilation surface. The ventilation opening penetrates the first and second surfaces and is aligned with the first ventilation surface. The first light source is arranged on the first base. The second light source is arranged on the second base.