Kosmos 27 (Russian: Космос 27 meaning Cosmos 27), also known as Zond 3MV-1 No.3 was a space mission intended as a Venus flyby. The spacecraft was launched by a Molniya-M carrier rocket from LC-1 at Baikonur on March 27, 1964. The Blok L stage and probe reached Earth orbit successfully, but the attitude control system failed to operate and so the stage could not be oriented properly for main engine start. It reentered the atmosphere one day after launch and burned up. Examination of telemetry data found that the failure was due to a design flaw in the circuitry of the BOZ unit, which resulted in power not being transferred to the attitude control jets on the Blok L stage.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets.