In the study of Self-Consistent Nuclear Energy System, the following 29 long-lived fission products (LLFPs) have been selected to be transmuted into stable or short-lived nuclides: 106Ru, 102Rh, 109Cd, 125Sb, 134Cs, 146,147Pm, 154,155Eu, 171Tm, 85Kr, 90Sr, 93mNb, 113mCd, 121mSn, 137Cs, 151Sm, 152Eu, 108mAg, 158Tb, 166mHo, 79Se, 93Zr, 94Nb, 99Tc, 107Pd, 126Sn, 129I, 135Cs. In the present study, the number of neutrons necessary for the transmutation of the 29 LLFPs with an FBR was evaluated, and the present status of the (n, γ) and (n,2n) cross section data of the 29 LLFPs in JENDL-3.2 and ENDF/B-VI was investigated. The main results of the present study are as follows: (1)only 0.25 neutron per fission is necessary for the transmutation of the 29 LLFPs with isotopic separation, whereas 6.8 neutrons are necessary with chemical separation, (2)the accuracy of the cross sections is 30 to 100% except for the (n, γ) cross sections of limited nuclides in limited incident neutron energy regions.