The Lambda 4S or L-4S was an experimental Japanese expendable carrier rocket.

It was produced by Nissan and the Institute of Space and Astronautical Science and launched five times between 1966 and 1970 with Ohsumi technology demonstration satellites.

[3] The Lambda 4S could place 26 kilograms (57 lb) of payload into low Earth orbit.

Following its retirement in 1970, a sounding rocket derived from it, the Lambda 4SC, flew three times in order to test technologies for the Mu rockets to follow.

The Mu replaced Lambda for orbital launches.