Ireland's Andrew Trimble, Paddy Wallace and Tom Court go straight into the starting line-up after being released from Six Nations duty.
Trimble takes up the right wing position, with youngster Craig Gilroy switching to the left wing and Scotland's Simon Danielli dropping to the replacements bench.
The returning Court takes over in the front row from Bryan Young and Wallace joins the in-form Nevin Spence at centre.
The other notable inclusions are Thomas Anderson, who is preferred to Willie Faloon in the back row, and Andi Kyriacou gets the nod at hooker ahead of Nigel Brady.
Johann Muller will again captain the side in the continued absence of Rory Best, who is in camp with Ireland along with Stephen Ferris.
Ulster boss Brian McLaughlin said: "It's great to have Andrew, Paddy and Tom back. It's great for them in that they're getting an opportunity to prove themselves and underline their worth to Declan (Kidney) as he sits down to name his team to face Scotland.
"So, it's a big game for them personally and it's a huge game for us as a team.
"We're going to the Scarlets, where Ulster have an appalling record, and we know we've got to play well if we're to get points."
Paddy Wallace added: "It's nice to get back with Ulster and get some game-time this weekend. It's a game we've got to win because we don't want to get too far down the table at this stage of the season.
"If we do that, it's going to be a long way back to get into that top four. So there's a lot of motivation from that point of view.
"From a personal point of view, you want to put yourself forward for selection for the Scotland game, so you want to play well knowing that Declan's going to be watching it."
ULSTER (v Scarlets): Adam D'Arcy; Andrew Trimble, Nevin Spence, Paddy Wallace, Craig Gilroy; Ian Humphreys, Ruan Pienaar; Tom Court, Andi Kyriacou, Declan Fitzpatrick, Johann Muller (capt), Tim Barker, Thomas Anderson, Chris Henry, Pedrie Wannenburg.
Replacements: Nigel Brady, Jerry Cronin, Bryan Young, Ryan Caldwell, Robbie Diack, Paul Marshall, Luke Marshall, Simon Danielli.