The Crystallization of amorphous silicon (α-Si:H) at lower temperatures is a challenging area of research these days because it will open up the possibilities of fabricating semiconductor devices like thin film transistors (TFT's), solar cells, active matrix liquid crystal display (AMLCD) devices at considearbly lower cost. Various metals e.g. Ni, Cu, Au, Ag and Al have been used to bring down the crystallization temperature of α-Si. We have found that aluminum assisted crystallization can bring down the temperatures of crystallization to as low as 200 °C. The crystallization behavior of α- Si:H has been studied by scanning electron microscopy, Raman spectroscopy, XPS spectroscopy and X-Ray diffraction but very little work has been carried out on microstructural investigation of the material using transmission electron microscopy. We have prepared specimen for die TEM study of α-Si:H and that of crystallized Si obtained by aluminum assisted crystallization. A detailed investigation of the crystallization behavior of α-Si:H using TEM have been carried out.