SummaryBackground We have demonstrated that carbohydrates in Cry j 1, the major allergen of Cryptomeria japonica pollen, play a major role in promoting Cry j 1‐specific Th2 response. However, little is known as to whether the carbohydrates directly participate in allergic responses.Objective We sought to determine whether Cry j 1‐related oligosaccharides function as IgE and/or T cell epitopes. In addition, the regulatory effect of Cry j 1‐related oligosaccharide on Cry j 1‐specific T cell responses was investigated.Methods Two monovalent oligosaccharides largely found on Cry j 1, Manα1‐6(Manα1‐3)(Xylβ1‐2)Manβ1‐4GlcNAcβ1‐4(Fucα1‐3)GlcNAc (M3FX), and GlcNAcβ1‐2Manα1‐6(GlcNAcβ1‐2Manα1‐3)(Xylβ1‐2)Manβ1‐4GlcNAcβ1‐4(Fucα1‐3)GlcNAc (GN2M3FX) were prepared. Manα1‐2Manα1‐6(Manα1‐2Manα1‐3)Manα1‐6(Manα1‐2Manα1‐2Manα1‐3)Manβ1‐4GlcNAcβ1‐4GlcNAc (M9A) was used as control. Competitive inhibition ELISA for Cry j 1‐specific IgE was performed using these oligosaccharides as inhibitors. In addition, T cell lines specific for Cry j 1 or purified protein derivative of Mycobacterium tubecurosis (PPD) were established, and cellular responses against these oligosaccharides were investigated in the presence or absence of the respective antigens.Results Overall, neither M3FX nor GN2M3FX displayed inhibitory effect on the binding between IgE and Cry j 1. In addition, M3FX did not by itself stimulate Cry j 1 or PPD‐specific T cells. However, M3FX significantly inhibited Cry j 1‐induced proliferation and IL‐4 production in Cry j 1‐specific T cells. Such an inhibitory effect was not seen in PPD‐specific T cell responses.Conclusion These results suggest that Cry j 1‐related oligosaccharides are not major epitopes for IgE or T cells. However, these oligosaccharides have a novel potential to inhibit Cry j 1‐specific T cell responses selectively.