Sagami Railway had made the Sotetsu 5000 series EMUs in 1955, but their short 18 meter frames were not large enough to carry the rapid increase of commuters that accompanied the Japanese post-war economic miracle.

Considering this population growth and aging of the 5000 series, Sagami planned new EMUs with larger bodies and flexible formations.

6021 prototype was successfully created and run using lightweight aluminum, which thereafter became the material of choice for many 6000 series body cars.

Sotetsu experimented with testing green and yellow colors for the trains.

The last use of the New 6000 series took place on 22 August 2003, with a special running of two trains on 12 November 2003.