Allergic rhinitis (AR) is a disease that presents with symptoms like nasal discharge, blockage, and itchiness, which impair the quality of life of most patients depending on its severity. The most common symptom in AR patients is a persistent bilateral nasal blockage, which may indirectly and potentially affect the airflow into the lung. However, the symptoms can be controlled using intranasal steroid spray (INS). This study investigated the role of nasal obstruction in lowering blood oxygenation and how INS improved blood oxygenation. This study included 33 patients with AR. Subjects with moderate-to-severe nasal obstruction were recruited based on the Visual Analogue Scale (VAS), and mometasone furoate nasal spray (MFNS) – two puffs twice a day for two weeks was given. Pre- and post-medication parameters compared included nasal obstruction VAS, partial oxygen arterial pressure (PaO2), partial arterial carbon dioxide pressure (PaCO2), and oxygen saturation (O2 saturation). All parameters were substantially different between pre- and post-medication. VAS, PaO2, PaCO2, and O2 saturation were significantly different before and after medicine (p<0.01). A comprehensive treatment of nasal obstruction using MFNS helps improve blood oxygenation and nasal obstruction in AR patients.