Hydrogen absorption mechanism in bulk MmNi(4.5)Al(0.5) (having a composition La 9.17%, Ce 17.43%, Pr 1.86%, Nd 5.34%, Ni 62.92% and Al 3.28%) was investigated by measuring in Situ electrical resistance under atmospheric pressure of hydrogen. It was observed that the resistance increases with an increase in hydrogen pressure. The effect of the number of cycles of hydrogen absorption on electrical properties of MmNi(4.5)Al(0.5) was also studied and P-C-T isotherms gave the hydrogen to metal ratio (H,'M) value of 1.0 at 2.06 x 10(5) Pa hydrogen pressure. In the attempts made to relate the content of hydrogen with changes in resistance, it was found that resistances of MmNi(4.5)Al(0.5) increases with increasing the hydrogen content.