A railcar air conditioning duct according to one aspect which guides air fed from an air conditioner mounted on a railcar. The railcar includes: a duct wall forming an air flow passage which guides air in a car longitudinal direction; and a plurality of through holes lined up in the car longitudinal direction, the through holes being open at the duct wall as air outlet ports through which the air in the air flow passage is blown from the air flow passage toward a passenger room. A ratio of an opening area of one of the through holes to an area of one of a plurality of partial regions formed by dividing, in the car longitudinal direction, an inner surface of a lower wall portion such that in plan view, the regions contain the respective through holes falls within a range of 2.0% or more and 7.5% or less.