Mythimna macrosaris is a moth of the family Noctuidae.

It was first described by Edward Meyrick in 1899.

It is endemic to the Hawaiian islands of Kauai, Oahu, Molokai and Hawaii.

The larvae mainly feed on Baumea meyenii, but have also been recorded feeding on Paspalum conjugatum, bunchgrass and sugarcane.

This Mythimnini-related article is a stub.