The Hansa-Brandenburg W.25 was a prototype floatplane fighter built by the Hansa-Brandenburg Aircraft Company () for the Imperial German Navy's () Naval Air Service () during World War I. It was a modified version of the company's single-seat KDW fighter, but it was not accepted for service.
The W.25 was an improved version of the single-seat biplane KDW with a modified single-bay wing with conventional inter-plane struts. It used a water-cooled Maybach Mb.III straight-six engine rather than the Benz Bz.III engine of the KDW. One prototype was built with ailerons only on the upper wing, but maneuverability was unsatisfactory. It was then modified with a second pair of ailerons on the lower wing connected to the upper ailerons by a strut. The armament consisted of two fixed, forward-firing LMG 08/15 machine guns.
The sole prototype of the W.25 was delivered to the Seaplane Experimental Command () in February 1918. It did not enter production because the Naval Air Service had lost interest in single-seat floatplane fighters by this time. The aircraft was then used as a training aircraft. It was located at Rügen-Bug when the Allies inspected the German seaplane bases in December 1918. Its ultimate fate is unknown, but it was likely scrapped.