Provided is a collapsible nasal-cavity spray catheter (6) made of a thermoplastic elastomer or other flexible and resilient material, which may be provided to a patient for operation by the patient and placement into the nasal cavity or nasopharynx (J). The catheter (6) comprises a catheter main body (61) and an adapter (62). The catheter main body (61) has a flat closed end (611), a transition section (TS) from the closed end (611) to a circular external-appearance part, a normal section (NS) having a circular external appearance, and an open end (612) opposite to the flat closed end (611)； a plurality of edge holes (613) are disposed near the closed end 611)； if the adapter (62) and a syringe (7) are fitted, it is possible to spray multiple powerful jets of water in the nasal cavity and nasopharynx (J) to clean out mucus and scabs. The maximum width of the transition section (TS) of the catheter main body (61) is not smaller than 1 mm, and the minimum thickness of its tube wall is not greater than 0.45 mm. Because of the flat closed end (611), transition section (TS), and collapsibility of the catheter main body (61), a catheter having a relatively large outer diameter may pass readily in a slit-shaped space, achieving preferable rinsing performance at narrow and deep areas while also preventing accidental insertion into the paranasal sinuses.
