Fijian winger Timoci Nagusa makes way in a rejigged back-line, with Paddy Wallace moving to full-back, Simon Danielli back on the left wing and Ian Whitten returning at centre alongside Darren Cave.
Up front, there are changes in all three lines. Bryan Young comes in for Declan Fitzpatrick at loosehead prop, Dan Tuohy is preferred to Ryan Caldwell in the second row and South African Robbie Diack will pack down at number 8.
Diack's inclusion sees team captain Chris Henry move to the openside flanker position.
Ulster Academy member Nevin Spence, who was a key figure in the Ireland Under-20s' Championship-winning side, could make his competitive debut for the province off the bench.
Commenting on Tuesday's clash with the Ospreys, Ulster assistant coach Neil Doak said: "With our last game against Cardiff providing a ten-day window to recover and prepare for the Ospreys on Tuesday night, it has given us the opportunity to get a few bodies back on board.
"We have to see how things work out with regards to fitness, but the aim is to push to win all the remaining games.
"We have two games at home and two away left, so we have got to make sure we are ready to put in a performance, in what is sure to be a very physical challenge tomorrow night.
"The Ospreys are on a mini-tour, they are out of the Heineken Cup, having narrowly lost to Biarritz on Saturday, so now they will be focused on getting a top four finish in the Magners League.
"We are expecting a high quality side to take the field tomorrow and we have to be ready to make our home advantage count.
"If we can get a few early points on the board, then we can settle into the game and play a bit of rugby," he added.
To purchase tickets for Ulster v Ospreys tie, you can click here, call the Ticket Line on tel: 028 90 493 222 (Option 2) or visit the Ticket Office at Ravenhill.
Tickets are also available from Ulster Rugby ticket outlets province wide. Tickets will be available to purchase on the gates tomorrow night from 6pm.
ULSTER (v Cardiff Blues): Paddy Wallace; Andrew Trimble, Darren Cave, Ian Whitten, Simon Danielli; Niall O'Connor, Isaac Boss; Bryan Young, Rory Best, BJ Botha, Ed O'Donoghue, Dan Tuohy, Stephen Ferris, Chris Henry (capt), Robbie Diack.
Replacements: Andi Kyriacou, Tom Court, Ryan Caldwell, David Pollock, Paul Marshall, Ian Humphreys, Nevin Spence.