Bursaphelenchus xylophilus (B. xylophilus) is a pine wood nematode that is known to cause pine wilt disease. We report here that B. xylophilus extracts augmented the polyclonal immunoglobulin E (IgE) production induced by lipopolysaccharide (LPS) plus interleukin-4 (IL-4) both in murine splenocytes and purified B cells as determined by ELISA and ELIspot assays, but they did not cause such a promotion in the absence of either LPS or IL-4. We also observed that the antigen-nonspecific IgE levels were increased in sera of mice treated with B. xylophilus extracts, which were comparable to those of Ascaris suum extracts. These findings suggest that administration of B. xylophilus extracts could suppress allergic diseases via a saturation of mast cell Fcε receptors or/and an inhibition of antigen-specific IgE synthesis to the allergen by a polyclonal response.