Acmenychus inermis is a species of beetle of the family Chrysomelidae. It is found in Azerbaijan, China (Xinjiang), Iran, Kazakhstan, Mongolia, Nepal, Russia, Turkey, Turkmenistan and Tadzhikistan.
Adults reach a length of about 5.5-6.5 mm. They have an elongate body and are completely black. The elytra have four raised ribs, each armed with curved spines.
The recorded host plants for this species are Phragmites communis and Phragmites australis.