| Kosmos 300 | |
| Operator: | Soviet space program |
| Cospar Id: | 1969-080A |
| Satcat: | 4104 |
| Mission Type: | Lunar sample-return |
| Spacecraft Type: | Ye-8-5 |
| Manufacturer: | GSMZ Lavochkin |
| Launch Date: | UTC |
| Launch Rocket: | Proton-K/D |
| Launch Site: | Baikonur 81/24 |
| Disposal Type: | Launch failure |
| Decay Date: | September 27, 1969 |
| Orbit Reference: | Geocentric |
| Orbit Inclination: | 51.5° |
| Orbit Period: | 88.2 min |
| Apsis: | gee |
| Programme: | Luna programme |
| Previous Mission: | Luna 15 |
| Next Mission: | Kosmos 305 |
| Programme2: | Kosmos (satellites) |
| Previous Mission2: | Kosmos 299 |
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 mission was a failure. The engines on the Block D upper stage failed due to an oxidizer leak, leaving the spacecraft to burn up in Earth's atmosphere.