A novel series of inhibitors that contain an aryl alpha,alpha-difluoro-beta-ketophosphonate group has been synthesized and evaluated against protein tyrosine phosphatase 1B. These compounds exhibit strong inhibitory activity, the best of which has a K(i) value of 0.17 microM. These results demonstrate that aryl alpha,alpha-difluoro-beta-ketophosphonates are powerful phosphotyrosine mimetics for the development of potent PTP inhibitors.