Magnetic tunnel junctions (MTJs) using epitaxially grown (100)-oriented and (110)-oriented Co2FeSi Heusler alloy bottom electrodes and amorphous Al-oxide barriers were fabricated. The tunnel magnetoresistance (TMR) ratios were 80% at 2 K and 48% at room temperature for the MTJ with the (100)-Co2FeSi bottom electrode. The MTJ with the (100)-Co2FeSi bottom electrode had a smaller TMR ratio than the MTJ with (100)-Co2FeSi electrode. The TMR ratio in MTJs with Co2FeSi electrode is smaller than that of a MTJ with Co2MnSi electrode. Tunnel conductance characteristics were investigated, revealing no half-metallic character in MTJs with Co2FeSi electrode in the conductance-voltage curves.