The author invented an ideal antrum-window operation as a simple intranasal surgery with double-flap window-plasty in the treatment of chronic maxillary sinusitis. This intranasal antrostomy with nasoantral window-plasty is the ideal technique in cases with mildly inflamed and reversible mucosa of the maxillary antrum, without polypoid and highly thickened mucosa, and the procedure also has the following advantages : 1) Prevents the postoperative occurrence of unpleasant complications such as cheek swelling, dental and labial numbness, disturbances of lacrimal passage due to over curettage, osteomyelitis and postoperative cheek cyst as in case had radical surgery. 2) The technique of two mucous flaps taken from the nasal cavity and the maxillary antrum covers the up-and down-margin of the window can prevent the postoperative bony bleeding and reclosing of the window due to over granulation, and consequently can keeps the permanently opened nasoantral window. 3) The operation is very simple and conveniently performed under local anesthesia and requires minimal hospitalization. 4) Minimum injury to the mucosa which rapidly returns to normal function. 5) High antroscopic visibility to determine the status of the sinal interior at all times during the surgery and the postoperative treatment. 6) In consideration on the view points of excretory function, ventilation and ciliary direction of the sinal mucosa, we believe that this intranasal antrostomy with nasoantral window-plasty is an ideal and better procedure than Boenninghaus's method in the choice of different plastic technique of the mucous flaps.