The flame retardant wool was prepared using zirconium oxychloride with various acids. The thermal degradation of wool treated with the flame retardant synergistic system, zirconium oxychloride, citric acid and hydrochloric acid, was studied by thermal analysis, mass loss, limiting oxygen index (LOI) and vertical flame test. The fabric surfaces were also observed by SEM. The wool treated with the flame-retardant shows an increase in the decomposition temperature, residual mass and LOI. Also the wool treated with hydrochloric acid showed improved flame retardant properties compared to the use of formic acid. The response surface methodology (RSM) was also used for the experimental plan with four variables on the results of flame retardancy. The statistical analysis confirms the optimum conditions obtained by the experimental results. (C) 2011 Elsevier B.V. All rights reserved.