An outdoor unit for an air-conditioning apparatus includes a casing having an air inlet through which air enters the casing, an air-sending device disposed in the casing and configured to create a flow of air passing through the air inlet, a heat exchanger disposed between the casing and the air-sending device and exposed through the air inlet and including a plurality of fins spaced apart from each other, and a partition disposed in the casing and dividing a space in the casing into an air-sending device chamber containing the heat exchanger and the air-sending device and a machine chamber containing a compressor. The plurality of fins include an end fin group located at an end remote from the partition. The casing includes a wall having at least one vent that faces the end fin group and that is located along a side edge part defining an edge of the air inlet.