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. We have been investigating the effect of ferromagnetism on the unconventional superconductivity of PrOs4Sb12 by substituting Nd for Pr. This proposal is aiming to use the zero-field muon-spin-relaxation measurements to continuing in monitor the evolution of broken time reversal symmetry in the Pr-concentrated side of the Pr1-xNdxOs4Sb12 system (x = 0.15 and 0.2).