Objective. Amyotrophic lateral sclerosis/parkinsonism-dementia complex is classified as one of the tauopathies. Methods. The total tau, phosphorylated tau, and amyloid β42 levels were assayed in cerebrospinal fluid from patients with Kii amyotrophic lateral sclerosis/parkinsonism-dementia complex (n = 12), Alzheimer's disease (n = 9), Parkinson's disease (n = 9), amyotrophic lateral sclerosis (n = 11), and controls (n = 5) using specific enzyme-linked immunosorbent assay methods. Results. Total tau and phosphorylated tau did not increase and amyloid β42 was relatively reduced in Kii amyotrophic lateral sclerosis/parkinsonism-dementia complex. Relatively reduced amyloid β42 might discriminate Kii amyotrophic lateral sclerosis/parkinsonism-dementia complex from amyotrophic lateral sclerosis and Parkinson's disease, and the ratios of phosphorylated-tau to amyloid β42 could discriminate Kii amyotrophic lateral sclerosis/parkinsonism-dementia complex from Alzheimer's disease. Conclusions. Cerebrospinal fluid analysis may be useful to differentiate amyotrophic lateral sclerosis/parkinsonism-dementia complex from Alzheimer's disease, amyotrophic lateral sclerosis, and Parkinson's disease.