Aldo will be making his sixth defense of the 145-pound title he claimed from Mike Brown on Nov. 18, 2009, while competing in WEC.
In his most-recent defense, the hard-striking Aldo (21-2) knocked out Chad Mendes in Round 1.
Koch (13-1) will enter the cage against Aldo on a four-fight win streak. His lone professional loss came against Mendes in March 2010.
UFC 149 will take place at Scotiabank Saddledome in Calgary, Alberta.