Here are some of his major works:
* The Poems of Heinrich von Kleist: A comprehensive English translation of Kleist's poetry, published in 1931.
* Heinrich von Kleist: A Biography: A detailed biography of Kleist, published in 1932.
* The Plays of Heinrich von Kleist: A collection of translations of Kleist's plays, including "The Prince of Homburg," "Penthesilea," and "The Broken Jug."
* The Romantic School in Germany: A survey of the German Romantic movement, published in 1933.
* Goethe: The Lyrical Poems: A translation of Goethe's poetry, published in 1951.
Zeydel also contributed articles and essays to various academic journals and anthologies. He was a respected scholar of German literature and his work has been praised for its accuracy, depth, and literary quality.