Amyloid β (Aβ) protein immunotherapy lowers cerebral Aβ and improves cognition in mouse models of Alzheimer's disease (AD). Here we show that Caribbean vervet monkeys (Chlorocebus aethiops, SK) develop cerebral Aβ plaques with aging and that these deposits are associated with gliosis and neuritic dystrophy. Five aged vervets were immunized with Aβ peptide over 10 months. Plasma and cerebral spinal fluid (CSF) samples were collected periodically from the immunized vervets and five aged controls; one monkey per group expired during the study. By Day 42, immunized animals generated plasma Aβ antibodies that labeled Aβ plaques in human, AD transgenic mouse and vervet brains; bound Aβ1–7; and recognized monomeric and oligomeric Aβ but not full-length amyloid precursor protein nor its C-terminal fragments. Low anti-Aβ titers were detected in CSF. Aβx-40 levels were elevated ∼2- to 5-fold in plasma and decreased up to 64% in CSF in immunized vervets. Insoluble Aβx-42 was decreased by 66% in brain homogenates of the four immunized animals compared to archival tissues from 13 age-matched control vervets. Aβ42-immunoreactive plaques were detected in frontal cortex in 11 of the 13 control animals, but not in six brain regions examined in each of the four immunized vervets. No T cell response or inflammation was observed. Our study is the first to demonstrate age-related Aβ deposition in the vervet monkey as well as the lowering of cerebral Aβ by Aβ vaccination in a non-human primate. The findings further support Aβ immunotherapy as a potential prevention and treatment of AD.