Stilbenes, especially those oligomers, have great potential to be antihyperglycemic agents. In this study, eight stilbene dimers, including five new ones, were obtained by biotransformation of piceatannol using Momordica charantia peroxidase (MCP) for the first time. Their structures were established on the basis of spectroscopic evidences. These piceatannol dimers displayed potential α-glucosidase inhibitory activities, and trans double bond, tetrahydrofuran ring, and free adjacent phenolic dihydroxyls were found to be important for their activities. Enzymatic biotransformation of stilbenes by M.charantia peroxidase (MCP) was showed to be a prominent way to produce oligomeric stilbenes for antihyperglycemic development.