Nuclear factor κ B (NF-κB) is involved in the pathogenesis of a number of neurodegenerative disorders with neuroinflammation. In order to clarify the role of NF-κB in ALS, immunohistochemical studies with an antibody that recognizes the p65 subunit of NF-κB were performed on the spinal anterior horn of 4 patients with sporadic ALS (sALS), 1 patient with optineurin-mutated ALS (OPTN-ALS), and 3 normal controls (NC). In patients with sALS or OPTN-ALS, the expression pattern of NF-κB was altered when compared to that of NC; NF-κB immunoreactivity tended to be absent from neuronal nucleus and was increased in microglia. The down-regulation of NF-κB in neuronal nucleus might contribute to a loss of neuroprotection, or neurons with nuclear NF-κB might be lost immediately after its activation. The microglial induction of NF-κB might contribute to neuroinflammation. In conclusion, NF-κB signaling pathway could have a key role in the pathomechanism of ALS.