He is remembered as the first publisher of the circa-1770 Lithuanian poem Metai (The Seasons) by Christian Donaleitis, now also known as Kristijonas Donelaitis. Rhesa collected and worked with the actual unpublished manuscript, which the widow of Donaleitis, Anna Regina, maiden name Ohlefant, had given to Pastor Johann Gottfried Jordan of Walterkehmen. He in turn gave it to Ludwig Rhesa. He also had a copy by Pastor J. F. Hohlfeldt of Gerwischkehmen available. Wilhelm von Humboldt urged him to do the translation and the book was finally published in 1818 under the title Das Jahr in Vier Gesaengen, literally "The Year in Four Songs"), along with German translation of Donaleitis' poems. It has since gone on to be translated into 16 more European languages.
Rhesa also researched the traditions of Baltic language folk song (daina). He published the first collection of 85 such songs in 1825 under title Dainos oder Litthauische Volkslieder. Thus he is considered to be the founder of Lithuanian folklore research.