You will need permission to do this if the material you are using is, for example, from commercially released material. Again, the relevant record companies and music publishers are likely to own the rights, so contact them for clearances. There have been Australian cases—in 2003 and 2005—in which courts have held that DJs and their labels had infringed copyright by recording and selling remixes of commercial music without permission from the owners of copyright in the material they had used. In each case, the DJs and their record companies had to pay not only legal costs, but also very large sums of money as compensation to the copyright owners.
You may, however, record and sell your own mixes if you write and record your own material, or only use licensed loops or samples.