PrOs4Sb12 is a 1.85 K superconductor. Its superconductivity shows unconventional behavior, and the originating mechanism remains unknown. One characteristic is an internal magnetic field detected in the superconducting state of PrOs4Sb12, which breaks the time-reversal symmetry and does not appear in conventional type superconductivity. The isostructure compound NdOs4Sb12 becomes ferromagnetically ordered below 0.9 K. We have been investigating the effect of ferromagnetic moment of Nd on the unconventional superconductivity of PrOs4Sb12. This proposal plans to use the zero-field muon-spin-relaxation measurements to monitor the evolution of broken time reversal symmetry in the series of Pr1-xNdxOs4Sb12.