An outdoor unit of an air conditioner is disclosed. The outdoor unit includes: a casing, including a portion defining an outlet through which air is discharged from the outdoor unit; an axial flow fan disposed in the casing for blowing air through the outlet, wherein the axial flow fan comprises: a hub; a plurality of main wings extending from the hub; and a rim connecting the main wings to one other and rotating integrally with the main wings; and one or more air entry blockers disposed at a clearance space between the rim and the portion of the casing defining the outlet.