Calreticulin (Crt) is a molecular chaperone ubiquitously present in the endoplasmic reticulum. In non-human primates, age-related occurrence of anti-Crt antibody has not been reported. We developed an ELISA assay for an anti-Crt antibody and determined the age-related increase in the levels of anti-Crt antibody in three groups of cynomolgus monkeys: juvenile (1.5 yr), young adults (5–10 yr) and aged adults (20–34 yr). Mean ± SD auto-antibody levels at 450 nm in juvenile, young adults and aged groups were 0.23 ± 0.18, 0.30 ± 0.28, and 0.55 ± 0.33, respectively. Statistically significant differences were noted in the autoantibody levels to Crt among the aged group and juvenile or young adults. This is the first report to demonstrate the expression of anti-Crt autoantibody in aged monkeys and indicates that cynomologous monkeys may serve as an appropriate nonhuman primate model for studies of age-related alteration of immune function in elderly humans. Though preliminary, this finding merits further investigation to determine the relationship between immunosenescence and expression of antibodies to Crt.