Oosthaven is a small harbour on the Nieuwe Merwede, adjacent to the Oostdijk in the Netherlands. Built in 1926–1927, it originally served as an agricultural loading and unloading quay.

The harbour is accessible via on- and off-ramps on either side, with the approach road connecting to the Nieuwe Merwedeweg.

A concrete-paved boat ramp, added at a later date, sits at the centre of the former quay, with the flanking areas occasionally used for parking. The harbour now functions primarily as a mooring for a houseboat, reachable from the entrance via a jetty.

Further access around or into the harbour is limited. Oosthaven is recognised as a municipal monument.