Magnetic tunnel junctions (MTJs) La0.7Sr0.3MnO3 (LSMO)/LaTiO3 /La2NiMnO6(LNMO)/Cr/Au were fabricated on SrTiO3 substrates to examine spin-filtering tunneling effect of the magnetic insulator LNMO by the measurement of tunnel magnetoresistance (TMR) through the ferromagnetic LSMO and LNMO layers. The crystal structures and magnetic properties of LNMO films were improved by growing them in high background oxygen pressure. The MTJ where the LNMO layer was prepared in oxygen pressure of 400 mTorr was found to show magnetoresistance ratio of about 10% at 50 K.