Core fistulectomy with endorectal advancement flap repair has been reported as a safe and effective technique for treatment of high fistula-in-ano. A number of rigid and flexible fistulectomy sets have already been fabricated pursuing the objectives of facilitating the procedure of this conservative surgical technique and reducing its risks of continence impairment. Two different methods (the method of scraping the granulation tissue of fistula and the method of separating and removing a thin layer from inside of tract) have been served in these sets for obliterating the abnormalities. In this work, with the aim of minimizing invasion to healthy tissue encircling the fistula, specially sphincter muscles, we designed and fabricated a new flexible fistulectomy device, which uses the second mentioned method. The new set separates an approximately 2.5-mm-thick layer from inside of the fistulous tract, by rotating a special tubular blade around its axis and moving the blade along the fistulous tract from external orifice toward the internal orifice. At the same time, the separated tissue may be removed from the fistulectomy lumen by rotating a special cannulated screw embedded coaxially inside the tubular blade. A flexible guidewire was used for identifying the tract path and guiding the device along it. We used the new set for excising 10 curved fistula models of approximately 16 cm length and 1.5 mm diameter, which were created in cubic pieces of fresh cow muscle as test specimens. After removing the device, each specimen was left with a smooth-walled lumen of approximately 9 mm diameter. The tubular blade works very well in separating a thin layer from inside of the fistula models and the cannulated screw is capable of easily removing the separated tissue. The removed tissue could be used as a sample of the whole tract for histopathological examinations. The screw and flexible guidewire lead the blade along the tract in a good manner and ensure circumferential separation of the fistula. With regard to the results of our tests, it is anticipated that the new set is an efficient instrument for easy, safe and fast core-out excision of high anal fistulas and is able to reduce the risk of injuries to healthy tissue encircling the fistulous tract.