Batsmen Max Holden and Joe Cracknell, all-rounder Martin Andersson and spinner Thilan Walallawita have all signed new contracts with Middlesex.
Holden, 22, Andersson, 24, and Walallawita, 22, have extended their stays until the end of the 2023 season.
Durham University student Cracknell, 20, has signed a deal until 2022.
"The youth that we have, mixed in with the senior talent here at the club, bodes really well for the future," said Middlesex head coach Stuart Law.
Holden has made 53 appearances for the county across all formats, while Cracknell and Walallawita made their first-team debuts this summer.
Meanwhile, batsman Dan Lincoln, 25, has been released by Middlesex after playing in six T20 Blast games last season.