Spotted fever is a rare acute and multisystemic febrile infectious disease with a mortality rate of ≥50% without adequate antibiotic treatment, and in diagnosed and treated cases, of approximately 2.5%. Currently, the applied test to diagnose this disease is the indirect immunofluorescence reaction, however two samples of paired sera are necessary to confirm the diagnosis, since using only one sample may allow for confusion with cross reactions. OmpA is an outer membrane protein present in the R. rickettsia, the etiological agent of spotted fever, able to activate dendritic and macrophage cells. It also presents immunogenicity properties, and is considered a target for the development of diagnostic tests for spotted fever. In this context, an amperometric immunosensor was developed for the identification of sera antibodies (human IgG) from patients with spotted fever aimed at improving sensitivity and minimize sample volume. The development of the immunosensor was conducted using a synthetic peptide, derivative from the H6PGA4 R. rickettsia protein, homologous to OmpA. Amperometric responses were generated at -0.6 to 0.6V, at a scan rate of 0.025Vs-1 for 20 cycles, a limit of detection of approximately 10ngmL-1 for the synthetic peptides and 0.01µgmL-1 for the humam serum, a sensitivity of 2.59µA, adequate for the detection of spotted fever antibodies. The construction of this immunosensor, capable of identifying circulating antibodies in real time, can also be applied in the diagnosis of other infectious-parasitic diseases.