OBJECTIVE To evaluate endoscopic ultrasonography for masses in nasal cavity and paranasal sinus. METHODS Under the guidance of nasal endoscope, sonographic scan of 18 masses within nasal cavity and paranasal sinus was performed by using 10 MHz catheter transducer with diameter of 3.3 mm under local anesthesia. Twelve of them were benign tumors and 6 of them were malignant ones, which were confirmed by pathological examination of resected specimens. RESULTS Under the guidance of nasal endoscope, masses could be observed accurately with catheter transducer. On gray scale ultrasound, most masses were heterogeneous hypoechoic, tumors with rich blood vessels were lower hypoechoic, and some showed irregular anechoic area due to dilated vascular net. Neurofibroma was with well-defined and regular border and entire capsule; chordoma was without distinct edge and capsule. A giant pituitary tumor eroding bone of sphenoid sinus and intruding into nasal cavity. The relationship between mass and internal carotid artery could be demonstrated using color Doppler flow imaging (CDFI). Blood flowing signals in masses could be detected by CDFI, and spectral Doppler could discriminate arterial or venous blood flowing signals and measure its velocity. The rich blood supply was observed in fibroangioma, the rich flow signals and high velocity could be detected in malignant tumors. CONCLUSIONS Nasal endoscope-guided sonography for soft tissue masses in nasal cavity is of exact location, clear image and high resolution, which can reveal blood flow signals sensitively, differentiate arterial and venous blood signals and measure the velocity of them. It provides a new imaging modality for masses within nasal cavity, sinuses and skull base.