We studied the segregation process of binary mixture of bronze disks. Equal masses of the different sized disks were put in a container subjected to an external vertical vibration. The velocity fields of both species were measured by an image processing system. The larger disks tend to move upwards and gather along the free surface and side walls. For the case with a smaller size ratio, two convective cells are apparent for both species. The larger size ratio mixture can reach the completely segregated state sooner.