Dear Sir :
I am very much regret to inform you that I have to resign my present position in your firm on the thirty-first of this month. The reason for this is that I have accepted a better position offered by an American firm on Patpong Road.
I should thank you very much if you would permit me to resign on the above-mentioned date, so that I shall be able to go to work at the new firm on the first of next month.
Yours faithfully