Conventionally, biodiesel is produced by the alkaline catalyzed transesterification of edible oils. The cost of these edible oils is quite high. Though the cost of waste and high free fatty (FFA) acid oils is almost one half to one third that of refined oils, the production cost increases due to additional steps for lowering the FFA to less than 2% for further transesterification to biodiesel. In this study, the esterification technique for the reducing FFA of rice bran oil (RBO) with 70% FFA using strong heterogeneous catalyst aluminum (Al) doped sulfated zirconia has been investigated. Several process affecting parameters like catalyst calcination temperature, stirrer speed, catalyst loading, oil to methanol molar ratio, reaction temperature and reaction time were optimized in order to minimize FFA of oil. The FFA conversion of 95.26% was achieved at 338.15 K, RBO to methanol molar ratio 1:9, catalyst loading 3 wt% in 180 min of reaction time. Consequently, this esterification step reduces the FFA of the oil and thus increases the possibility of producing biodiesel at lower price.