Kosmos 300 (Russian: Космос 300 meaning Cosmos 300) (Ye-8-5 series) was the fourth Soviet attempt at an uncrewed lunar sample return.

It was probably similar in design to the later Luna 16 spacecraft.

It was launched, on a Proton rocket, on September 23, 1969.

The engines on the Block D upper stage failed due to an oxidizer leak, leaving the spacecraft to burn up in Earth's atmosphere.

This article about one or more spacecraft of the Soviet Union is a stub.