No, not directly. It only allows the raspi's 3.3V inputs and outputs work with 5V sensors and the like, and it probably won't handle enough current to drive a relay.
To drive a relay you'd need something that could handle a bit more current, like a transistor or a ULN2003 chip or something. Here's one post:
http://www.raspberrypi.org/phpBB3/viewt ... 37&t=10130
In there someone lnked to this example (don't try the mains wiring bit though!):
http://www.susa.net/wordpress/2012/06/r ... sing-gpio/
But there are lots more examples if you can find them in the "Projects" forum sections.