A 12-year-old girl was admitted to the authors' hospital due to muscle weakness, gait disturbance, dysarthria, dysphagia, and diplopia. She experienced prodromal fever 10 days before admission. On examination, deep tendon reflex was absent in the extremities, and nerve conduction velocity was decreased in the ulnar nerve. She was diagnosed with Guillain-Barré syndrome (GBS). Despite steroid pulse therapy following administration of intravenous high-dose γ-globulin, clinical manifestations remained unchanged. Therefore, plasma exchange was performed on day 10 of the illness. The titer of serum Mycoplasma immunoglobulin M level was increased. Immunological testing was positive for serum anti-galactocerebroside C antibody. On day 18 of the illness, however, she developed generalized convulsion. Brain magnetic resonance imaging revealed high intensity in the medial temporal lobes, including the hippocampus and thalamus on T2-weighted intensity imaging, which was consistent with limbic encephalitis. Further immunological tests revealed positivity for anti-N-methyl-D-aspartate-type glutamate receptor antibody in the cerebrospinal fluid. She was treated with additional plasma exchange; however, she exhibited residual manifestations including short-term memory disorder, emotional incontinence, and convulsions. This article describes a notable case of limbic encephalitis following GBS associated with prodromal Mycoplasma infection. It is interesting that autoimmune encephalopathy is concomitant with autoimmune polyneuropathy subsequent to Mycoplasma infection.