Soy sauce (Shoyu) is a traditional fermented seasoning of East Asian countries and is available throughout the world. We obtained polysaccharides from raw soy sauce, and showed the anti-allergic activities of these Shoyu polysaccharides (SPS) in vitro and in vivo. The present study determined whether oral supplementation of SPS is an effective intervention for patients with seasonal allergic rhinitis. In an 8-week randomized, double-blind, placebo-controlled parallel group study, patients with mild seasonal allergic rhinitis were treated with 600 mg of SPS (n=25) or placebo (n=26) each day. After 4 weeks of treatment with SPS, symptom scores such as sneezing, nasal stuffiness, and hindrance of daily life were significantly different (P<0.05) from those in placebo-treated groups. The total symptom score, calculated from the sum of individual scores, showed a significant difference (P<0.05) between the 2 groups after 4-8 weeks. On nasal examination by the investigator, the color of the inferior turbinate in SPS-treated patients was significantly different (P<0.05) from that in placebo-treated patients between weeks 4 and 8, and the nasal symptom scores for color of inferior turbinate, watery discharge, and state of sniffles were also significantly different (P<0.05) from those in the placebo-treated group after 8 weeks. In conclusion, SPS of soy sauce improved the quality of life of patients with seasonal allergic rhinitis, and soy sauce would be useful in an anti-allergic therapy utilizing daily foods.