No, it supports Crossfire and not SLI.
SLI usually works on nvidia chipsets......
The Manufacturer says it does not support SLI but others say it does support SLI, that is something that has got me wondering where the truth lies......
Well, if you want to get the final word then here it says it is SLI capable...... but I have a GD70 and that is certainly not SLI capable.....
http://forum-en.msi.com/index.php?topic=141092.0
Even Vendors are claiming it to be SLI capable.....
http://www.pricebat.ca/MSI-P55A-GD55-P55-LGA1156-ATX-DDR3-2xPCIe16-3xPCIe1-2XPCI-SLI-CrossFireX-SATA3.p_10196419/