With Paddy Wallace on Six Nations duty with ireland, Ian Whitten gets a chance to partner the in-form Nevin Spence at centre. Ruan Pienaar and Ian Humphreys continue their half-back partnership.
With both Rory Best and Tom Court unavailable due to international commitments, Nigel Brady, Bryan Young and Declan Fitzpatrick complete the province's front row.
Tim Barker comes in to partner captain Johann Muller in the second row, with Dan Tuohy sidelined by a quad tear.
Chris Henry and Willie Faloon, who return from O2 Ireland Wolfhounds duty, join Pedrie Wannenburg in a robust back row combination.
Fresh from helping the Wolfhounds to victory over England Saxons, out-half Ian Humphreys is relishing a return to Magners League action.
"The Ospreys are a good team. Dan Biggar will probably be playing number 10 and he runs the show," said Humphreys, who has played 49 times for Ulster in the Magners League and Heineken Cup.
"In Marty Holah and Jerry Collins they have a couple of class players in the pack. They are like us, they have a big squad and international call-ups really don't affect them.
"We know it is going to be tough, but we have plenty of confidence, we have won a lot of our games recently and even the tight games we are managing to pull through now, which we might have lost in the past.
"The confidence is there and the leadership that we have got through the foreigners and just the experience of our local lads is giving us the confidence for the big games."
Humphreys is confident that Ulster can put it up to the defending league champions, despite missing the injured Stephen Ferris and the Ireland-tied Paddy Wallace and Rory Best.
"In the past few years, maybe our team was over reliant on the likes of Ferris, Best and Wallace, but now with the South Africans brought in and the experience the other players are starting to get, it's not a big blow to us.
"The fact we lose (Andrew) Trimble and can bring in Craig Gilroy, who has scored five tries in three games, is not the worst.
"These are the times we target to get a lot of points because we have invested heavily in our foreigners, so they would be available for this kind of time period.
"It's important that they play well and there is no doubt they will. We have a strong squad now and the international call-ups don't hurt us as much as in the past."
ULSTER (v Ospreys): Adam D'Arcy; Craig Gilroy, Nevin Spence, Ian Whitten, Simon Danielli; Ian Humphreys, Ruan Pienaar; Bryan Young, Nigel Brady, Declan Fitzpatrick, Johann Muller (capt), Tim Barker, Chris Henry, Willie Faloon, Pedrie Wannenburg;
Replacements: Andi Kyriacou, Jerry Cronin, Alan Whitten, Ryan Caldwell, Thomas Anderson, Paul Marshall, Luke Marshall, David McIlwaine.