The Ireland hooker has been sidelined since injurying his ankle against Leinster on December 26 and will make a welcome return to provincial duty before the Ireland Six Nations training camp next week.
Williams has selected a dramatically different back-line with four personnel changes and one positional switch. Bryn Cunningham drops out of the matchday 22, leaving Australian Mark Bartholomeusz to get the nod at full-back.
Tommy Bowe and new Ulster recruit Mark McCrea fill the wing berths, while Ravenhill favourite Paul Steinmetz is back at inside centre.
Ballymena centre Seamus Mallon has been named on the replacements bench for his first involvement in an Ulster matchday squad since October. Paddy Wallace and Isaac Boss will form the half-back partnership with Niall O'Connor and Kieran Campbell both benched.
Up front, Ireland prop Bryan Young returns to the starting line-up alongside Best and Declan Fitzpatrick, with Tom Court and Nigel Brady the back-up front rowers.
Delighted to have his captain back on the pitch, Williams said: "It is great to have Rory back and a good chance for him to stake his claim for a place in the Irish side.
Meanwhile, former Wallaby Justin Harrison also returns to the Ulster team alongside Ryan Caldwell in the second row.There is no change in the back row from the Bourgoin game with Neil McMillan providing cover on the bench.
ULSTER (v Gloucester): Mark Bartholomeusz; Tommy Bowe, Andrew Trimble, Paul Steinmetz, Mark McCrea; Paddy Wallace, Isaac Boss; Bryan Young, Rory Best (capt), Declan Fitzpatrick, Justin Harrison, Ryan Caldwell, Matt McCullough, Neil Best, Grant Webb.
Replacements: Nigel Brady, Tom Court, Carlo Del Fava, Neil McMillan, Kieran Campbell, Niall O'Connor, Seamus Mallon.