Soyuz 20 (Russian: Союз 20, Union 20) was an uncrewed spacecraft launched by the Soviet Union.

It was a long-duration test of the Soyuz spacecraft that docked with the Salyut 4 space station.

Soyuz 20 performed comprehensive checking of improved on-board systems of the spacecraft under various flight conditions.

Living organisms were exposed to three months in space.

The primary goal of the mission was to test hardware modifications to the Soyuz 7K-T spacecraft that would extend its operating life from two to three months in preparation for long-duration Salyut crew residencies.