This paper considers the design and validation of a model of an industrial batch process in TiO2 production. The model will be used for flexible recipe control, which is a model-based approach used in control and optimisation of batch processes. Because of insufficient knowledge and a lack of proper data, different process models were developed: a semi-empirical dynamic model based on chemical kinetics laws, and several experimental black-box models. In the paper the models are validated and mutually compared. Validation of models has shown that besides comparing the model and the process output behaviour, additional measures considering also the model input error should be introduced for proper model validation related to the model use. In our case, introducing additional measures also contributed to improvement of the model design procedure, so that a simple yet satisfactory black-box model was obtained despite a small amount of process data. (c) 2004 Elsevier Ltd. All rights reserved.