The Mitsubishi Ki-1 was a low-wing, cantilever monoplane with fixed landing gear, twin fins and rudders, and was powered by two 701 kW (940 hp) Ha-2-2 water-cooled radial engines, giving a maximum speed of 220 km/h (140 mph). The pilot and co-pilot were seated in tandem under an enclosed canopy, while gunners sat in semi-enclosed nose and dorsal gun turrets, each armed with a single 7.7 mm (.303 in) machine gun. The usable bomb load was up to 1,500 kg (3,310 lb).
The Ki-1 shared a similar configuration with the Junkers S36 first flown in 1927. Militarized into the Junkers K37 by Junker's Swedish subsidiary AB Flygindustri at Limhamn near Malmö, it was able to reach altitudes not reachable for the fighters of 1927. However, as soon as 1930 this advantage was lost due to British developments such as the Bristol Bulldog fighter, and Junkers was not successful in selling the design. In 1931 however representatives of Mitsubishi Nainenki K. K. from Japan visited the Limhamn facilities to study some of the military conversions of Junkers aircraft. The sole K37 prototype S-AABP (ex D-1252 S36-prototype), as well as all development papers were purchased in part by funds raised by donations in Japan. The aircraft got the name Aikoku No.1 (patriotic gift). In any case, the wing design of the Ki-2 was essentially the same as that of the Junkers, with some modifications, but the Ki-1 itself shared nothing whatsoever with the German design other than a similar appearance.
The K37 prototype was brought to Japan and tested in combat during the Manchurian Incident of 1931, following which the Imperial Japanese Army Air Force authorized Mitsubishi to produce both heavy and light bomber variations. The heavy bomber version, Ki-1, was much larger than the original Junkers K37 and first flew in August 1932. A total of 118 aircraft were built in two versions between March 1933 and April 1936.