ABSTRACT In this study an incident plane electromagnetic wave in free space and in ZnO NPs is numerically simulated using 1D FDTD method. The simulation of the propagation of plane wave in ZnO NPs is compared with the simulation of the propagation of plane wave in free space. The electric and magnetic field variations were numerically calculated in both free space and in ZnO NPs by discretizing Maxwell’s equations. For electrical conductivity of 7x10 -6 S/m and 1.5x10 S/m the numerical simulation of the plane wave in ZnO NPs shows the propagation of plane wave does not attenuate, because the conductivity of ZnO NPs is very small. However, the magnitude of electric and magnetic fields in ZnO NPs is attenuated for large electrical conductivity of 0.04 S/m and ZnO NPs absorb both electric and magnetic fields. -5