The Paul Martin Sr. Building is a 6-storey Art deco low-rise office building in Windsor, Ontario, Canada, located on the west side of Ouellette Avenue between Chatham Street and Pitt Streets.

Major renovations along with a four-storey addition were completed in 1959 to expand post office operations.

The building's limestone façade was in very poor condition and contained many chips and cracks visible from the street.

Some exterior features contributing to the heritage value are the bronze plaques identifying "Post Office" and "Customs and Excise", a stone band above the first floor with carved "Dominion Public Building" and "Post Office" along with Canadian Crests.

The Windsor Public Library has been temporarily relocated to the building after selling their former location to the Downtown Mission.