The interaction of amorphous silicon (a-Si) and aluminum (Al) has been examined using in-situ transmission electron microscopy. Carbon coated nickel grids were used for depositing thin (∼50nm) amorphous silicon films using ultra high vacuum cluster tool and a thin film of Aluminum (∼50nm) was deposited subsequently on a-Si film by sputtering. The grid containing a-Si and Al films was mounted on a heating holder of FEI 200kV TEM and loaded in the TEM for viewing the microstructural and phase transformations during the in-situ heating process. The microstructural features and electron diffraction patterns in the plain view mode were observed with increase in temperature starting from 30 °C to 275 °C. The temperatures used in this experiment were 30,100,150,200, 225, 275°C . A sequential change in microstructural features and electron diffraction pattern due to interfacial diffusion of boundary between Al and amorphous Si was investigated. Evolution of polycrystalline silicon with randomly oriented grains as a result of a-Si and Al interaction was revealed. After the in-situ heating experiment the specimen was taken out and etched to remove excess of Al and the subjected to high resolution imaging under TEM and EDS analysis. The EDS analysis of the crystallized specimen was performed to locate the Al distribution in the crystallized silicon. It has been shown that Al induced crystallization can be used to convert sputtered a-Si into polycrystalline silicon as well as nanocrystalline silicon at a temperature near 275 °C by controlling the in-situ annealing parameters. The mechanism of AIC has been discussed from the experimental results and the phase diagram of Al-Si system.