Japanese cedar pollinosis is an important contributor to allergic rhinitis in Japan. Lactobacillus may be useful as an immunomodulator and is used widely as a foodstuff. The purpose of the study was to examine the effects of daily intake of the Lactobacillus paracasei strain KW3110 in patients with cedar pollinosis. The effects of daily intake of KW3110 in patients with cedar pollinosis were investigated in 126 patients who received KW3110 or a placebo in a double-blind study. The study began 1 month before the start of the pollen season and lasted for 3 months. A significant reduction of nasal symptoms and the serum level of eosinophil cationic protein and improvement of quality of life scores occurred in the patients who received KW3110 when pollen scattering was low. However, the effects were limited during the peak period of pollen scattering. Intake of KW3110 may reduce allergic inflammation, but the effect is limited.