They come back, along with skipper Simon Easterby, after being rested for the away game against the Ospreys on December 27.
Coach Nigel Davies is eager that the New Years Day home clash against the Newport Gwent Dragons sees a return to the winning way which saw off the Cardiff Blues at Parc y Scarlets on December 20.
Jones replaces young in-form fly-half Rhys Priestland, Rees comes in for Mahonri Schwalger and Easterby starts at flanker in place of Vernon Cooper who suffered a back injury against the Ospreys.
Right-wing Gareth Morris keeps his place after a useful debut at the Liberty Stadium.
Coach Davies told a Parc y Scarlets press conference (on Monday): "The Dragons are a very good, combative side who play to their strengths and who have a strong, experienced pack.
"They're aggressive, will look to take us on in the set-piece and in the last couple of games have been very opportunistic with the chances they've had. If you switch off for a moment they'll hurt you. It'll be tough for us because it's difficult to get anything from the Dragons - we'll just have to build a performance."
On the return of big names such as Jones, he said: "Our resources have been challenged this season, primarily through injuries, so people like Steve have had to play a hell of a lot of games.
"Steve is a class act but he's played more rugby than any professional in Wales this season and he needed a rest. We had full confidence in Rhys Priestland for the Ospreys game and he had an excellent game.
"Because of our injuries this season, players like Rhys have had opportunities and people like Johnathan Edwards, Phil John, Ken Owens, Lou Reed, Dominic Day, Martin Roberts and Jon Davies have come through well. That's very encouraging and positive as we move forward."
Scarlets: Starting XV v Dragons - 15 Morgan Stoddart, 14 Gareth Morris, 13 Regan King, 12 Jon Davies, 11 Mark Jones, 10 Stephen Jones, 9 Martin Roberts; 1 Phil John, 2 Matthew Rees, 3 Deacon Manu, 4 Dominic Day, 5 Simon Maling, 6 Simon Easterby (c), 7 Johnathan Edwards, 8 David Lyons.
Replacements - 16 Craig Cross, 17 Mahonri Schwalger, 18 Lou Reed, 19 Dafydd Jones, 20 Gavin Cattle, 21 Rhys Priestland, 22 Darren Daniel.
Guinness PRO12
Suite 208, Alexandra House,
The Sweepstakes
Ballsbridge, Dublin 4, Ireland