ADAMs (a disintegrin and metalloproteinase) have important roles in development and diseases such as cancer. Previously, an ADAM15 splice variant (ADAM15B), which contains an inserted cytoplasmic Src-binding site, was linked to clinical aggressiveness in breast cancer, yet little was known about how this splice variant affects the function of ADAM15. Here, we show that ADAM15B has enhanced catalytic activity in cell-based assays compared with ADAM15A, which lacks a Src-binding site, using shedding of fibroblast growth factor receptor 2iiib variant as an assay for catalytic activity. Moreover, the enhanced activity of ADAM15B compared with ADAM15A depends on Src because it is abolished by Src-kinase inhibitors and in Src(-/-) cells, but not in Src(-/-) cells rescued with Src. These findings provide insights into the mechanism of how a splice variant linked to clinical agressiveness in breast cancer causes increased activity of ADAM15B, and suggest that inhibitors of the ADAM15 protease activity or of the interaction of ADAM15B with Src could be useful to treat breast cancer in patients with dysregulated ADAM15B.