This document describes the design and analysis of a two-stage reduction gearbox for an all-terrain vehicle. It discusses the components, methodology, modeling, and analysis of the gearbox. The gearbox was designed with gears, shafts, bearings and a casing using CAD software. Finite element analysis was performed to analyze stresses on gears and shafts. Computational fluid dynamics was used to analyze oil flow inside the gearbox. The results showed the gearbox design is efficient and improves upon current designs by being lighter, more compact and durable. Further optimization of the design is possible by integrating additional components to simplify the powertrain assembly.