In the present study a bleaching process of a kaolin of industrial interest was carried out using thiourea as the leachant agent in the iron removal process. The beneficiation of kaolin, by iron removal, improves its economic value, and it is then possible to use it in the ceramic and paper industries. The effect of thiourea was investigated together with other factors, such as sulphuric acid concentration, temperature and treatment time. Full factorial experiments were performed to determine the main and interaction effects on the iron dissolution from the mineral: the largest iron extraction yield (94%) was obtained after 150 min. of treatment at 90°C, 0.25 M H 2 SO 4 and with 10 g/l of thiourea. At the same temperature the iron extraction yield was 68% after 120 min. of treatment with 0.1 M H 2 SO 4 and 1 g/l thiourea. An empirical model of data fitting was used in order to evaluate the optimal conditions of the process, considering as factors the treatment time and the thiourea concentration. The experimental results show the technical feasibility of this process for the removal of iron from kaolin used in the experimental tests.