We have preliminarily evaluated the reduction of prediction errors of the core characteristics of the breeding light water reactor core based on the bias factor method by utilizing the FCA critical experiments carried out for MOX fueled tight lattice light water reactor cores. The prediction error of k eff is reduced from 0.62% to 0.40% by utilizing the FCA-XV-2 (45V) and (65V) results. As for the reaction rate ratio of 238U capture and 239Pu fusion, it is found that the FCA-XV-2 (80V) result is suitable for the upper core and the upper blanket of the real core and the FCA-XXII-1 (65V) and XV-2 (65V) results are suitable for the lower core and the internal blanket.