Choi devised the modern order of the Hangeul letters, and assigned names to the letters. His most famous book on Hangeul is the Hunmong Jahoe (훈몽자회; 訓蒙字會 "Collection of Characters for Training the Unenlightened", 1527).
Choi was an official interpreter in the Korean embassies in Beijing, so he also documented colloquial northern Chinese languages.