A centrifugal fan includes an impeller and a housing. The housing includes an upper plate, a lower plate and a side wall, wherein the upper plate axially corresponds to the lower plate, a side wall is formed between the upper plate and the lower plate, an axial inlet is formed on the upper plate, a lateral outlet is formed on the side wall, the impeller is disposed in the housing and corresponds to the inlet, and a flow path communicates the inlet to the outlet. The housing further includes a guiding groove, and at least one auxiliary inlet is formed in the guiding groove.