A procedure for the quantitative phase analysis (QPA) using the whole-powder-pattern fitting methods was applied to eight- to ten-component mixtures of ceramic materials. Accuracy in the QPA using the whole-powder-pattern decomposition (WPPD) method and the Rietveld method was examined. Average deviations of the calculated weight fractions of respective phases using the WPPD method from those prepared by mixing were within 0.5 mass%, and they were smaller than those obtained by using the Rietveld refinement. Minor phases (-1 mass%) in ten-component samples were analyzed, and their weight fractions could be measured within the error of less than 0.1 mass% by using the WPPD method. Rapid QPA using the WPPD method was also tested.