  We report on the properties of central engines in the $\gamma$-ray blazars
located at high redshifts beyond z~>~0.4, where the extra-galactic background
light (EBL) starts affecting their $\gamma$-ray spectra. The physical engine
that provides power to the blazars of very high bolometric luminosity is
assumed to be a highly collimated jet of matter moving relativistically away
from the supermassive black hole (SMBH), located in the central region of the
host galaxy, in a direction aligned toward the Earth. Due to their peculiar
geometry and special physical conditions, blazars at redshifts beyond z~>~0.4
are bright enough to be detected in the $\gamma$-ray energy band. In this work,
we investigate the physical properties of high-$z$ $\gamma$-ray blazars
detected by the Large Area Telescope (LAT) on board the \emph{Fermi} satellite.
We also study the properties of their emission regions and the central engines
and discuss cosmological and astrophysical implications.
