Although it is anecdotally known that nasal obstruction is associated with snoring, it remains unknown whether the application of nasal steroids could decrease oral/oro-nasal breathing and increase nasal breathing, and subsequently decrease snoring indices. This study evaluated the effect of nasal budesonide on breathing route pattern and snoring. Twenty-four snorers were enrolled in a randomized, double-blind, crossover trial of 1-week treatment with nasal budesonide compared with 1-week intervention with nasal placebo. At the start and end of each treatment period, patients underwent nasal resistance measurement and overnight polysomnography with concomitant measurement of breathing route pattern and snoring. Twelve patients were randomly assigned to a 1-week treatment with nasal budesonide, followed by 2-week washout period and a 1-week intervention with the nasal placebo; and 12 patients were randomly assigned to a 1-week intervention with nasal placebo, followed by 2-week washout period and a 1-week treatment with nasal budesonide. Nasal budesonide was associated with a decrease in oral/oro-nasal breathing epochs and concomitant increase in nasal breathing epochs, decrease of snoring frequency by [median (interquartile range)] 15.8% (11.2–18.8%), and an increase of rapid eye movement sleep; snoring intensity decreased only in patients with increased baseline nasal resistance by 10.6% (6.8–14.3%). The change in nasal breathing epochs was inversely related to the change in snoring frequency (Rs = 0.503; P < 0.001). Nasal budesonide in snorers can increase nasal breathing epochs, modestly decrease snoring frequency and increase rapid eye movement sleep.