Background: Chlamydia pneumonia has currently been proposed to be involved in multiple sclerosis (MS) pathogenesis. The aim of this study was to evaluate the serum level of anti-C. pneumoniae immunoglobulin G (IgG) in patients with MS compared to the control group, which may be helpful in further understanding of MS etiology. Methods: The serum was obtained from 66 people with MS and 20 healthy people as patient and control groups, respectively. Serums were matched to the patient’s age, gender, and place of residence. Finally, anti-C. pneumoniae IgG was measured by a sandwich enzyme-linked immunosorbent assay (ELISA). Results: Sixty-six patients (25 men and 41 women within the age range of 17-56 years and mean±SD of 35.53±9.56) with MS and 20 control subjects (8 men and 12 women with the age range of 25-56 and mean±SD of 38.3±9.66) were enrolled in this study. The mean serum anti-C. pneumoniae IgG of patients with MS (28.82±33.54 RU/mL) was compared with that of the control group (4.075±6.691 RU/mL) and a statistically significant difference was observed in this regard (P<0.001). Conclusions: In general, there was a significant relationship between the incidence of MS and the C. pneumoniae infection. However, the actual involvement of C. pneumoniae in MS is still a matter of debate and needs to be clarified in further studies (e.g., by creating animal models and conducting trial tests).