We study the properties of gluons in QCD in the maximally abelian (MA) gauge. In the MA gauge, the off-diagonal gluon behaves as the massive vector boson with the mass M-off similar or equal to 1.2 GeV, and therefore the off-diagonal gluon cannot carry the long-range interaction for r much greater than M-off(-1) similar or equal to 0.2 fm. The essence of the infrared abelian dominance in the MA gauge is physically explained with the generation of the off-diagonal gluon mass M-off similar or equal to 1.2 GeV induced by the MA gauge fixing, and the off-diagonal gluon mass generation would predict general infrared abelian dominance in QCD in the MA gauge. We report also the off-diagonal gluon propagator at finite temperature.