A hybrid model based batch-to-batch control strategy is proposed for control of particle size distribution (PSD) in cobalt oxalate synthesis process. In order to enhance the model prediction accuracy and generalization capability, a hybrid modeling approach for cobalt oxalate synthesis process in cobalt hydrometallurgy is developed by combining simplified first principle model with PLS model. The simplified first principle model that captures the dominant characteristics of the synthesis process is built to describe PSD evolution. The PLS model is utilized to compensate the unmodeled characteristic of the simplified first principle model and to enhance model generalization capability. Due to the repetitive nature of the process, a batch-to-batch control strategy based on hybrid model is then presented to design the operating policy that drives the process to a target PSD. Applications to a simulated cobalt oxalate synthesis process demonstrate that the proposed approach can improve process performance from batch to batch in the presence of unknown disturbances. (C) 2012 Elsevier B.V. All rights reserved.