A middle-aged male suffering from encephalopathy with cerebral amyloid angiopathy (CAA) with amyloid beta (Aβ) presented with initial symptoms of transient consciousness disturbance and left visual field photophobia. Lesions with aberrantly high signal on T2-weighted magnetic resonance imaging (MRI) of the brain appeared in the right temporal lobe posterior to the occipital lobe and spread to other areas. Brain biopsy revealed Aβ deposits in vascular walls and numerous diffuse plaques in parenchymal areas. Based on MRI findings, Initial corticosteroid therapy with beta methasone effectively improved the neurological symptoms of consciousness disturbance and motor deficits. After corticosteroid therapy was stopped at 4 weeks, recurrence occurred. Additional corticosteroids did not improve clinical symptoms and the patient progressed to a bed-ridden state with a severe consciousness disturbance. Notably, CSF Aβ1-42 and CSF Aβ1-40 decreased while the recurrent encephalopathy worsened. After intense deterioration, the patient became stable. CSF Aβ1-42 increased but remained at a very low level. This case of CAA encephalopathy with apolipoprotein E ϵ4/ϵ4 homozygosity showed Aβ deposits in vascular walls and numerous diffuse plaques in parenchymal areas. The clinical course suggests that reduction of CSF Aβ1-42 and Aβ1-40 might be related to clinical deterioration in cases of encephalopathy.