New toilet facilities will also be created as well as an extended space for women to worship.
However, the plans have not been met favourably with several people living nearby voicing their objections.
Concerns include increased traffic, more noise, privacy invasion from the new build and smells from the toilet block.
All the residents of Charles Street have written a joint letter to Gloucester City Council expressing their concerns.
The main issues they raise are parking issues and the proximity of the building to homes.
Barton resident Joe Kilker said: “This was never a mosque in the first place and now it is creeping towards being a very large one. Before that happens, I believe the council needs to address this ‘change of use’.”
There are already mosques in All Saints Road, Conduit Street and Ryecroft Street.
Gloucester city councillor Said Hansdot (L, Barton and Tredworth) said: “I can understand the residents’ views. Traffic and parking is a problem everywhere.
“All mosques have the same issues with residents, like parking, noise etc.”
Consultation on the plans ends on October 26.