National letters of Annam are diplomatic and trading letters between Vietnam and Japan in the Seventeenth century. Many researchers studied these documentary sources
however, there are still some details which have yet to be elucidated. The article attempts to determine the number of letters between the two sides and the authors of the letters from Vietnam (15 letters from Tonkin, 30 from Cochinchina). 23 letters from Japan, and 2 letters with undetermined location and date. About the authors, the letters from Tonkin were written by the Trjnh Lords and some government officials
meanwhile, the letters from Cochinchina were of the Nguyen Lords, and the author demonstrates that most of them were written by Lord Nguyen Phuc Nguyen.