A process for preparing a rubber composition comprises: (a) forming a mixture of: (i) at least one thiocarboxyl-functional hydrolyzable silane, (ii) at least one rubber containing carbon-carbon double bonds, (iii) at least one silane-reactive filler, (iv) at least one activating agent, and (v) water; (b) mixing the composition formed in step (a) under reactive-mechanical-working conditions and in the absence of vulcanizing agent(s); (c) adding at least one vulcanizing agent (vi) to the composition of step (b); (d) mixing the composition of step (c) under non-reactive-mechanical-working conditions; and, (e) optionally, curing the rubber composition of step (d).