The ATV transmission system comprises a CVT gearbox along with the axles and hubs which in turn drives the vehicle. The gearbox coupled with CVT provides optimal torque and power at all times. This paper focuses on the design and optimization of a two-stage reduction gearbox for BAJA All-Terrain Vehicle. Based on the CVT’s high- and low-end ratios and different road resistances, the required reduction ratio of the gearbox is calculated. Also, the gradeability factor and maximum acceleration required were the factors taken into account for determining the reduction ratio. Standard AGMA procedures were utilized to scrutinize the design of gears and shafts by using force equations. © 2021, Springer Nature Singapore Pte Ltd.