Aim: Although there are several auxiliary laboratory tests, diagnosis of acute appendicitis (AA) mainly depends on clinical findings. The aim of this study was to evaluate the role of ischemia-modified albumin (IMA) in the diagnosis of AA. Methods: IMA levels of histopathologically confirmed AA cases and healthy volunteers were evaluated. Results: Mean IMA levels were 9.6 ± 12.5 absorbance units (ABSU) in the AA group and 3.04 ± 0.47 ABSU in the control group. Moreover, IMA levels positively correlated with the diagnosis of AA (r = 0.309, P = 0.013). The preoperative mean IMA level was 9.6 ± 12.5 ABSU, while the postoperative mean IMA level was 6.9 ± 11.7 ABSU (P = 0.001). There was a significant decrease in IMA levels after appendectomy. Conclusion: This study shows elevated IMA levels in patients with AA and a significant decrease of IMA levels after appendectomy. Oxidative stress plays a role in the pathogenesis of AA, and IMA levels can be used as an accessory parameter in diagnosis.