Welsh open-side flanker Merriman is seen as a great young prospect after captaining his national U21s side at Kingsholm against England in this year's Six Nations.
The 20 year-old back-row forward has signed a new two-year contract that will see him compete for a place in the starting line-up for the coming season.
21 year-old Nick Wood has also agreed new terms with the Kingsholm club. The loose-head prop, who has been an ever-present with the England U21s over the last year, was in impressive form during the recent IRB World Championships. The 6ft prop has signed a new two-year contract.
Scrum-half Alex Page has also signed up for next season on a one-year deal. The 23 year-old was a regular in the Gloucester team during the World Cup last season, and alongside Simon Amor, he added options at half back.
Gloucester will kick off their Heineken Cup campaign in October when they take on Stade Francais in Paris.