atoid Inflammation of the synovial joints causes damage to the joints and functional impairment in people with arthritis (RA), a chronic autoimmune illness. Apoptotic process dysregulation in immune cells, especially macrophages, may contribute to RA pathophysiology. An intriguing protein that has recently come to light as a possible contributor to the onset and development of RA is Apoptosis Inhibitor of Macrophage (AIM)/CD5L. Evidence from research points to a link between AIM/CD5L expression and RA disease activity. Serum and synovial tissues from people with active RA show higher levels of AIM/CD5L, suggesting that it may be a biomarker for disease activity. Methods: The 120 participants in this case control research were split into three groups according on their diagnoses: group A consisted of 60 patients with RA, group B of 30 patients with OA, and group C of 30 seemingly healthy individuals who were age and sex matched to the other two groups. People were scouted from Benha University Hospitals' rheumatology, physical medicine, and rehabilitation outpatient clinics and patient departments. The results showed a statistically significant difference (P<0.001) in the mean serum AIM levels in RA patients (1292.1 ng/ml), OA patients (691.7 ng/ml), and healthy controls (483.7 ng/ml). With a diagnostic capacity at its peak at 654.09ng/ml, serum AIM may distinguish between RA patients and healthy persons with remarkable specificity and sensitivity. In conclusion, serum AIM has the potential to become a novel RA biomarker.