C-13 MAS NMR has been performed in situ to investigate the mechanism of toluene alkylation with methanol (MeOH) or dimethyl ether (DME) at 433 K over H-ZSM-11 catalyst. The reaction protocol used allowed to separate the main reaction stages : MeOH and DME adsorption, activation, and reaction with toluene. In both cases, five strongly bound species were identified upon activation at 433 K,namely, MeOH and DME side-on and end-on adsorption complexes and methoxy species. End-on adsorbed complexes and methoxy species were found to be reactive in toluene alkylation, the reactivity of end-on adsorbed complexes being much higher.