A ventilation system comprises a ventilation fan with a lamp and a ceiling which has an installation opening. The ventilation fan with the lamp is adapted for installing to the ceiling through the installation opening. The ventilation fan comprises a housing, a fan module, and a lamp module. The housing includes a top plate and a side wall which are connected with each other to form a first opening. The first opening is aligned with the installation opening. The fan module is disposed in the housing. The lamp module is disposed out of the installation opening. The lamp module and the housing are located at opposite sides of the installation opening of the ceiling. The lamp module includes a light source, a base, at least one optical component, a switch and a lamp cover. The optical component and the switch are disposed at the different sides of the base.