The ASU-85 is the successor to the ASU-57, the first Soviet post-war airborne anti-tank gun. It was designed with many components of the PT-76 amphibious tank and is characterized by a highly sloped glacis plate and hull sides which are of all-welded construction. In contrast to the open-topped design of the ASU-57, the superstructure is fully enclosed with an armored roof which enabled it to feature NBC protection. Armor protection, however, is light at just 40 mm maximum in order to keep the weight down; it is still over four times heavier than the ASU-57 but benefited from the availableilty of larger helicopters like Mi-6 and Mi-10, as well as multi-chute and retro-rocket systems. Armament is significantly improved compared to its predecessor, featuring a 85-mm D-70 gun that is mounted on the glacis plate, slightly offset to the left of the hull. This gun was based on the wartime guns used on the T-34 and SU-85 but fires more powerful HE, APHE, and HVAP rounds. Other equipment includes an infra-red searchlight and features a splash plate for improved fording, even though the amphibious capability of the PT-76 was removed. Soon after its introduction, the ASU-85 replaced the ASU-57 in service with Soviet airborne forces throughout the 1960s until it was replaced by the BMD series. Export users included East Germany and Poland.

Development was undertaken by the same design bureau as the ASU-57, led by Nikolia Astrov and a prototype was known as the Ob'yekt 573. Production was delayed in order to provide it with an armored roof, which was missing in its original design, and the first units were not ready until 1961 as the ASU-85. No variants were developed.