Portal axle is a type of gearbox, especially used in off-road vehicles. Excessive contact and bending pressures lead to gear tooth failure. Spur and Helical gear trains without idler have taken for the analysis. Gear trains are modeled in SOLIDWORKS and analyzed in ANSYS workbench software. Gear materials for this study include steel, cast iron, and Aluminium alloy. In this study, contact stresses and bending stresses of spur and helical gear are theoretically calculated using Hertzian theory and Lewi's formula for all the three materials. The corresponding analysis is carried out using Finite Element Analysis (FEA). The results from theoretical calculation and FEA analysis is compared with each other. It is observed the results from both theoretical calculations and FEA analysis are in good agreement with each other. It is observed that stress induced on the spur gear made up of Aluminium alloy is less in comparison with all the other combinations. Fatigue analysis on spur gear made up of Aluminium alloy is carried out.