Indole is a benzopyrrole resulting from the fusion of a benzene ring on (α) and (β) carbons of pyrrole. It is a substance that is related to a great number of natural compounds, which play a considerable biochemical role.  . The theoretical study of Fischer reaction, which is a general way of indole synthesis, was carried out by means the semi-empirical (AM1, PM3 and MNDO) and ab-initio methods (STO-3G, 3-21G, 6-31G and 6-31G*) to analyze the three mechanisms proposed for this reaction. Energies and heats of formation obtained are based on primarily on geometries optimization calculation for different hypothetical intermediates in the three mechanisms. Transition states calculations allows the clarification of Fischer reaction regioselectivity. The comparative theoretical study made on the proposed mechanisms, shows that the Robinson’s mechanism is the most favorable.