Smith, 35, who signed a one-year contract last summer, will not be offered a new deal and Brentford will not be taking up the option to extend Proschwitz’s contract.
Proschwitz, 28, joined Brentford from Hull last August and scored three goals in 29 appearances. Smith scored once in the 32 games he featured in.
The club’s four on-loan players – Betinho, Chris Long, Alex Pritchard and Jon Toral – will be returning to their parent clubs, while goalkeeper Richard Lee has retired.
Lee, 32, who made 87 appearances, announced his intention at the start of 2015.
Bees trio Will Grigg, Sam Saunders and Nico Yennaris – who finished the season out on loan – will report back for pre-season training with the club in July.