The invention provides a process for preparing a filled halobutyl elastomer, which includes mixing a halobutyl elastomer with at least one mineral filler that has been reacted with at least one organic compound containing at least one basic nitrogen-containing group and at least one hydroxyl group and, optionally, with at least one silazane compound before admixing the filler with the halobutyl elastomer and optionally curing the filled elastomer with sulfur or other curative systems.