Intranasal corticosteroid therapy has exhibited effectiveness for improving nasal symptoms and quality of life (QOL) scores associated with seasonal allergic rhinitis. We prospectively investigated the efficacy of mometasone furoate nasal spray (MFNS) for improving the total nasal symptom score, QOL score, and sleep quality in subjects with perennial allergic rhinitis (PAR). Nasal airway conditions were also objectively assessed by measuring nasal nitric oxide (NO). Fifty-seven patients with PAR were randomized to MFNS or placebo for a 14-day, double-blind, crossover study. The subjects recorded their symptoms on nasal symptom forms and a visual analog scale. QOL and sleep quality were surveyed in accordance with the Japanese version of the Rhinoconjunctivitis Quality of Life Questionnaire (JRQLQ) and the Japanese version of the Epworth Sleepiness Scale. Nasal NO was measured during a single exhalation using a chemiluminescence analyzer. MFNS treatment achieved significant reductions versus placebo for total nasal symptoms (p < 0.001). There were significant decreases of the usual daily activity domain (p < 0.005), outdoor activities (p < 0.01), social function (p < 0.05), and the overall QOL score (p < 0.05) of JRQLQ with MFNS therapy versus placebo. A significant reduction of the sleepiness scale was also observed in the MFNS group with high sleep disturbance (p < 0.01). A significant decrease of nasal NO was found in the MFNS group (p < 0.01), especially among patients with severe nasal symptoms (p < 0.005). This prospective study indicated that MFNS therapy significantly improves nasal symptoms, QOL, sleep quality, and upper airway condition in Japanese subjects with PAR.