The purpose of this study is to determine the profile of cognitive impairment of ALS using neuropsychological test batteries and ERP measures. We examined 19 sporadic ALS; 8 patients had a spinal, 11 had a bulbar onset of the disease. We compared ALS with normal controls (NCs) that were matched sex, age, and education. Neuropsychological signature was assessed by MMSE and WCST. We also performed correlative studies with respiratory function and clinical acuity (using ALSFRS-R). The auditory “oddball” stimulation was presented and recorded from 20 channels and global field power (GFP) and peak latency of GFP were determined. MMSE score, resulted in more than 24, revealed no obvious dementia of all patients. In ERP study, the prolongation of N1/N2/P3 latency compared with NC was recognized. In correlative study, vital capacity positively correlated with P3 amplitude and negatively with P3 latency. In addition, we found negative correlation between clinical acuity and P3 amplitude, and negative correlation between the acuity of bulbar symptoms and P3 latency. Our findings supported that a reduction of prefrontal function exists in ALS patients, although respiratory failure may also influence cognition indicated by abnormalities of ERP components regardless of ALS subtype.