Ataxic Guillain-Barré syndrome (GBS) associated with anti-GQ1b IgG antibody has been reported. We, however, have had a patient with ataxic GBS who had IgG antibodies to the minor gangliosides GM1b and GalNAc-GD1a, and we therefore retrospectively investigated the clinical features of patients who had antibodies to GM1b or GalNAc-GD1a, but not to GQ1b. Information on patients' antecedent illnesses, initial symptoms, neurological signs, and CSF findings was reviewed in those with ataxic GBS or Fisher syndrome (FS) with anti-GM1b or anti-GalNAc-GD1a IgG antibodies. We tested whether the anti-GM1b and anti-GalNAc-GD1a antibodies are cross-reactive and constructed three-dimensional structural models of GM1b and GalNAc-GD1a. Ataxic GBS was diagnosed in 1 of 65 patients who had both anti-GM1b and anti-GalNAc-GD1a antibodies and in 3 of 159 patients who had anti-GM1b antibody without anti-GalNAc-GD1a antibody: FS was diagnosed in 1 of the 159 patients and in 1 of 35 who had anti-GalNAc-GD1a antibody without anti-GM1b antibody. All the patients' antibodies to GM1b or GalNAc-GD1a were associated with the IgG isotype. The clinical features of patients with ataxic GBS associated with anti-GM1b or anti-GalNAc-GD1a IgG antibodies did not differ from those of patients who had anti-GQ1b IgG antibody. Absorption study findings for serum from the patient who had both anti-GM1b and anti-GalNAc-GD1a IgG antibodies showed significant absorbance of anti-GM1b IgG antibody by GalNAc-GD1a and of anti-GalNAc-GD1a IgG antibody by GM1b, indicating that these antibodies are cross-reactive. This is the first report of ataxic GBS or FS associated with anti-GM1b or anti-GalNAc-GD1a IgG antibodies. These autoantibodies, as well as anti-GQ1b IgG antibody, may function in the development of some patients with ataxic GBS and FS.