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The Fermi gamma-ray satellite has recently detected gamma-ray emissions fromradio galaxy cores. From these samples, we first examine the correlationbetween the luminosities at 5 GHz, L_{5GHz}, and at 0.1-10 GeV, L_{gamma}, ofthese gamma-ray loud radio galaxies. We find that the correlation issignificant with L_{gamma} \propto L_{5GHz}^{1.16} based on a partialcorrelation analysis. Using this correlation and the radio luminosity function(RLF) of radio galaxies, we further explore the contribution of gamma-ray loudradio galaxies to the unresolved extragalactic gamma-ray background (EGRB). Thegamma-ray luminosity function is obtained by normalizing the RLF to reproducethe source count distribution of the Fermi gamma-ray loud radio galaxies. Wefind that gamma-ray loud radio galaxies will explain ~25% of the unresolvedFermi EGRB flux above 100 MeV and will also make a significant contribution tothe EGRB in the 1-30 MeV energy band. Since blazars explain 22% of the EGRBabove 100 MeV, radio loud active galactic nuclei (AGNs) population explains~47% of the unresolved EGRB. We further make an interpretation on the origin ofthe EGRB. The observed EGRB spectrum at 0.2-100 GeV does not show an absorptionsignature by the extragalactic background light. Thus, the dominant populationof the origin of EGRB at very high energy (>30 GeV) might be nearby gamma-rayemitting sources or sources with very hard gamma-ray spectrum.

Contribution of the Gamma-ray Loud Radio Galaxies Core Emissions to the Cosmic MeV and GeV Gamma-Ray Background Radiation