A process is described for producing an M41S family molecular sieve. The process comprises preparing a synthesis mixture capable of forming said molecular sieve in a reactor, which is equipped with a mixer having a Froude number of at least 1, said synthesis mixture having a solids content of at least 20 wt %. The synthesis mixture is heated in the reactor while agitating the mixture with said mixer to form a product mixture comprising water and crystals of said molecular sieve material. Thereafter at least part of the water is removed from the product mixture in the reactor so as to decrease the water content of the product mixture inside the reactor by at least 5 wt %.