This was the eighth Soviet spacecraft launched to return lunar soil to Earth. It was evidently sent to complete the mission that Luna 18 had failed to accomplish.

After a 4.5-day flight to the Moon, which included a single midcourse correction on Feb. 15, Luna 20 entered orbit around the Moon on Feb. 18. Initial orbital parameters were 62 x 62 miles (100 x 100 kilometers) at 65 degrees inclination. Three days later, at 19:13 UT, the spacecraft fired its main engine for 267 seconds to begin descent to the lunar surface. A second firing further reduced velocity before Luna 20 set down safely on the Moon at 19:19 UT on Feb. 21, 1972 at 3 degrees 32 minutes north latitude and 56 degrees 33 minutes east longitude, only about a mile (1.8 kilometers) from where Luna 18 had crashed.
After collecting a small sample of lunar soil, the spacecraft's ascent stage lifted off at 22:58 UT on Feb. 22 and quickly accelerated to about 6,000 miles per hour (2.7 kilometers per second) — a velocity-sufficient to return to Earth. The small spherical capsule eventually parachuted down safely on an island in the Karkingir River, about 25 miles (40 kilometers) north of the town of Dzhezkazgan, Kazakhstan, at 19:19 UT on Feb. 25, 1972.

The 2-ounce (55-gram) soil sample differed from that collected by Luna 16 in that the majority (50 to 60 percent) of the rock particles in the newer sample were ancient anorthosite (which consists largely of feldspar) rather than the basalt of the earlier one (which contained about 1 to 2 percent of anorthosite). Like the Luna 16 soil, samples of the Luna 20 collection were shared with American and French scientists.