Alan Connell, Jonathan Smith, Mattia Lanzano and Lee Cox have all been made available for transfer by Swindon.
The quartet have been placed on the transfer list by Robins boss Paolo Di Canio having been deemed surplus to requirements at the County Ground.
Striker Connell joined the club for an undisclosed six-figure sum from Grimsby last summer and Town's decision to part with his services comes as a surprise given he went on to top the club's scoring charts in his first season, bagging 13 goals in 44 appearances in all competitions.
Smith was another summer signing 12 months ago, going on to make 48 appearances in total, as was goalkeeper Lanzano, who went on to enjoy seven outings.
Fellow midfielder Cox, who also played seven times last term, only joined the club in January on a two-and-a-half year deal from Inverness for an undisclosed fee.
Meanwhile, Lukas Magera has seen his contract with Swindon cancelled by mutual consent.
The striker, 29, arrived at the County Ground last summer and went on to score once in 18 appearances in all competitions for Town last season.
However, he did not make a single appearance after January and ended the season back on loan at former club Banik Ostrava.
Di Canio has already added seven new faces to his squad this summer, despite Town clinching the npower League Two title last season.