Kal Naismith heads the list of departures as Kenny Jackett plots Pompey progress.
But Brandon Haunstrup and Alex Bass are remaining at Fratton Park.
In addition, talks are being held to keep Adam May, while Christian Oxlade-Chamberlain’s contract could be extended as he recovers from injury.
Yet it is Naismith who is the most prominent name to emerge after the Blues failed to agree a fresh deal with the 26-year-old.
The Scot, one of the pivotal figures of last year’s League Two title triumph, now leaves Fratton Park as a free agent.
Naismith made 94 appearances and scored 21 times for the Blues after arriving in May 2015 from Accrington.
He is joined through the exit door by Nicke Kabamba, Jez Bedford and Theo Widdrington.
Kabamba has seen loan service at Colchester and Aldershot this season, yet struggled to make an impact away from Pompey.
Signed in January 2017 from non-league Hampton & Richmond, the striker made six appearances for the Blues.
His final outing was as a substitute appearance in the 1-1 draw with Walsall in August.
Academy products Bedford and Widdrington have spent loan time in non-league football this season.
Midfielder Widdrington made 22 appearances and scored three times at the Hawks before recalled early from a mooted season-long stay.
He sat on Pompey’s bench for eight matches during the club’s injury problems, but was never called upon to enter the action.
Meanwhile, attacking-midfielder Bedford represented Poole Town 32 times this term, netting five goals.
Like Widdrington, he was recalled by Pompey in the face of a lengthening injury list, heading back in mid-February.
Fellow academy product Oxlade-Chamberlain broke his leg in training last month and is out of contract.
However, the Blues are in discussions over a fresh deal while he recovers.
The 20-year-old spent a sizeable period on loan at Oxford City, where he played against Notts County in the FA Cup.
Talks are also taking place with May, who this term featured 18 times for the Blues. Jackett is eager to retain the out-of-contract midfielder, who enjoyed a breakthrough season with the
Elsewhere, Pompey have taken up club options on Bass and Haunstrup, keeping them at Fratton Park for another 12 months.
Left-back Haunstrup made 19 appearances this season, while Bass earned his Football League debut in Saturday’s win over Peterborough.
Loanees Stephen Henderson, Matty Kennedy, Stuart O’Keefe, Connor Ronan, Anton Walkes and Tareiq Holmes-Dennis have returned to their parent clubs.
Pompey will now assess whether to pursue further interest in them.