Johann Muller misses the round 7 match having suffered a calf injury, so Jared Payne is named as captain - a role he last took on in the pre-season win over Leinster.
The New Zealander will start at full-back in place of Stuart Olding who is also unavailable as he was concussed during last weekend's bonus point victory over Cardiff.
Trimble starts on the right wing with Michael Allen selected on the left. Darren Cave and Chris Farrell are paired togerher in midfield, with Ruan Pienaar moving from scrum half to out-half and Paul Marshall donning the number 9 jersey.
In the front row, the only change sees Rob Herring picked at hooker with John Afoa and Callum Black selected on either side.
There is a whole new second row with Lewis Stevenson and Neil McComb starting, while in the back row Wilson moves from the back of the scrum to openside flanker, Robbie Diack keeps his place on the blindside and Nick Williams returns at number 8.
The game is live on the BBC Sport NI website and on S4C - Channel 120 - Freesat viewers; Channel 166 - Virgin TV; Channel 134 - Sky.
Ulster's next home fixture is against Edinburgh on Friday, November 22. More than 11,000 tickets have already been sold for that match. Tickets are available to purchase online here.
ULSTER (v Scarlets): Jared Payne (capt); Andrew Trimble, Darren Cave, Chris Farrell, Michael Allen, Ruan Pienaar, Paul Marshall; Callum Black, Rob Herring, John Afoa, Lewis Stevenson, Neil McComb, Robbie Diack, Roger Wilson, Nick Williams.
Replacements: Niall Annett, Kyle McCall, Ricky Lutton, Mike McComish, Sean Doyle, James McKinney, Ricky Andrew, David McIlwaine.