Kinetics of hydrogen absorption and desorption reactions was investigated on the MgH2 composite doped with 1 mol% Nb2O5 as a catalyst by ballmilling. The composite after dehydrogenation at 200 °C absorbed gaseous hydrogen of ~ 4.5 mass% even at room temperature under lower pressure than 1 MPa within 15 sec and finally its capacity reached more than 5 mass%. On the other hand, the catalyzed MgH2 after rehydrogenation desorbed ~6 mass% hydrogen at 160 ºC under purified He flow, which followed the first order reaction. From the Kissinger plot, the activation energy for hydrogen desorption was estimated to be ~71 kJ/molH2, indicating the product was significantly activated due to the catalytic effect of Nb2O5.