Pranlukast (PLK) is a leukotriene receptor antagonist (LTRA) that has been approved for treatment of asthma in patients of all ages and allergic rhinitis (AR) in adults but not for AR in children in Japan. This randomized, double-blind, placebo-controlled, crossover study used an artificial exposure chamber (OHIO Chamber) to investigate the efficacy and safety of PLK in children from 10 to 15 years old with seasonal AR (SAR) due to Japanese cedar (JC) pollen. Eighty-four subjects were enrolled and randomized to the treatment arm and 74 were included in the per protocol set. Subjects received either PLK dry syrup (DS) or placebo for 1 week. They were challenged with JC pollen in the OHIO Chamber for 3 hours. Total nasal symptom scores (TNSSs) were recorded every 30 minutes during the exposure. PLK DS treatment suppressed the TNSS changes from baseline significantly when compared with placebo. The difference in the least square means in TNSS between the PLK DS-treated group and placebo group was -0.37 (95% CI, -0.54, -0.20) with a value of p < 0.0001, showing that PLK DS significantly suppressed the nasal symptoms. Regarding specific nasal symptoms, PLK DS significantly suppressed sneezing, nasal discharge, and nasal obstruction. The effect of PLK DS on nasal obstruction was most prominent, with significant improvement relative to placebo beginning 60 minutes after the start of exposure. No serious adverse events were reported during the study. In this study, PLK DS is effective and safe for treatment in children with SAR.