Bellator officials announced the fight Friday. The 185-pound contest will headline Bellator 185 on Oct. 20 at Mohegan Sun Arena in Uncasville, Connecticut.
Mousasi (42-6-2) signed with Bellator earlier this week. A former UFC contender, he exited the promotion on a five-fight winning streak.
ESPN.com ranks Mousasi as the No. 5 middleweight in the world. Fighting out of Amsterdam, Mousasi has said he is eyeing titles at middleweight and light heavyweight.
Shlemenko (56-9), of Russia, is unbeaten since 2014. He has 31 career wins by knockout.