Diffusion of Co in Zr＿46.75Ti＿8.25Cu＿7.5Ni＿10Be＿27.5 bulk metallic glass under high pressure is investigated in supercooled liquid regio n by ion implantation combined with secondary ion mass spectroscopy.Before impla ntation of Co atoms,the amorphous samples were annealed and relaxed in supercool ed liquid region.Diffusion coefficients of Co at 603K in the relaxed samples are found to increase with increasing pressure.And the activation volume for diffus ion is obtained to be -1.236Ω,where Ω is the mean atomic volume of the alloy.The result shows that diffusion of Co in this case is in an interstitial way.