The influence of temperature (in the range of 2—390K) on the magnetic moment,and magnetoresistance has been investigated in this paper. It is found that the magnetoelectric properties, particularly the Curie temperature TC, th e metal-insulator transition temperature, Tmi, and the maximum m agnetoresistance TMR, of La0.8Ba0.2MnO 3 are closely related to the valence of Mn in the oxides. La0.８Ba０.2M nO3 synthesize d with 2+ Mn oxides exhibited the lower resistivity, and a Curie temp erature c loser to room temperature (290K) compared with that synthesized with 3+ Mn ox ides. It can be concluded that the magnetoelectric properties of La0.8Ba 0.2MnO3 are dependent on the Mn valence of oxides. This cou ld be attribut ed to the influence of oxygen vacancy concentration variation on the Mn4+ /M n3+ ratio in the resultant compounds during solid sintering react ion, which results from the valence difference of oxide precursors.