Deposition of polysilicon at low temperatures is important for the low cost production of electronic devices, especially solar cells and active matrix liquid crystal displays (AMLCD). In this paper in situ X-ray diffraction studies of aluminum enhanced crystallization of hydrogenated amorphous silicon (a-Si:H) at low temperatures is reported. Hydrogenated amorphous silicon films were deposited on oxidized silicon substrates. Aluminum was deposited on the a-Si:H using evaporation. X-ray diffraction analysis was done in an evacuated temperature controlled camera at a glancing angle of 5 degrees using thin film optics. Growth in the [111] silicon peak was monitored while annealing the samples at 200, 225, 250 and 275 degrees C, Results show that the area under the [111] silicon peak grows linearly with time. The rate of crystallization was found to be higher at higher temperatures. Al-induced crystallization was found to follow an Arrhenius type dependence. The activation energy for the thermally activated phenomenon controlling crystallization was calculated to be 1.1 eV. This is close to the reported activation energy of 1.2 eV for the diffusion of Al in a-Si:H.