Shear band is the key feature that controls the plastic deformation process of metallic glasses (MGs). However, the investigation directly on the shear band and its properties is rarely conducted as the band is perceived as extremely narrow. We have conducted a controlled experiment to form a single shear band in the specimen, which enabled us to probe shear-induced softening and dilatation directly on the shear band itself. Extreme dilatation and free volume increase as high as 1.14% and 1.40% respectively, have been observed, resulting from a drastic structure change due to severe plastic flow in the band. Nanoindentation on the individual shear band reveals significant softening of 36% and an unexpected wide width up to 160 μm, three magnitudes higher than what has been reported. These prove beyond doubt the dilatation as a mechanism for softening. The correlation between the free volume content and softening is discussed. Our findings provide a new insight for understanding the deformation behavior of metallic glass.