IgG anti-GQ1b antibodies are a powerful serological marker for the diagnosis of Fisher syndrome (FS), but little is known regarding serological markers in FS patients that do not have the autoantibodies. The authors analyzed IgG antibodies against gangliosides other than GQ1b, ganglioside complexes, and ganglioside-like lipo-oligosaccharide (LOS) of Campylobacter jejuni isolates from FS patients. We identified 24 (12%) patients with GQ1b-seronegative FS among 207 FS patients who had been referred to our laboratory for anti-ganglioside antibody testing. Patients with GQ1b-seronegative FS were male and had a history of antecedent gastrointestinal illness more frequently than FS patients with IgG anti-GQ1b antibodies. Other clinical features during the illness were not distinguishing for GQ1b-seronegative FS. Four (17%) of 24 patients with GQ1b-seronegative FS had IgG antibodies against single gangliosides such as GM1b, GD1a, or GT1a. Antibodies against GM1 and GT1a complex were detected in four GQ1b-seronegative FS patients, three of whom did not have antibodies against single gangliosides. Mass spectrometry analysis showed that C. jejuni isolates from FS patients had GD1c-, GalNAc-GM1b-, or GalNAc-GD1c-like LOS, and not GQ1b-like LOS, highlighting the utility of examining serum antibodies against these ganglioside mimics in GQ1b-seronegative FS patients. Seven (29%) had IgG antibodies against the LOS from C. jejuni strains expressing GD1c-, GalNAc-GM1b-, or GalNAc-GD1c-like LOS. These findings suggest that IgG antibodies against GM1b, GD1c, GalNAc-GM1b, and ganglioside complexes are serological markers for GQ1b-seronegative Fisher syndrome.