Abstract Background: Many complications arise as a result of delayed diagnosis and treatment of complicated acute appen-dicitis (CAA). C-reactive protein (CRP), white blood cell (WBC) count and procalcitonin (PCT) are among of the biochemical indicators that are utilized to improve the clinical prediction of acute appendicitis (AA). Aim of Study: The aim of this study is to assess how useful serum PCT as a predictor for complicated acute appendicitis diagnosis, in order to help doctors make better decisions. Patients and Methods: A total of 100 individuals who underwent open appendectomy from December 2017 to March 2021 in Tanta University Hospital, were included in this prospective cohort research. Upon admission, each patient had CRP, serum PCT, and Alvarado score assessment. Results: There was a positive relationship between serum PCT and CRP (r=0.279, p=0.048). The optimum cutoff value was 1.07ng/ml, 30mg/l. PCT had a sensitivity of 85.71% and a specificity of 81.4%. For identifying patients with CAA using binary logistic regression analysis with CRP and PCT as independent variables. PCT elevation remained an inde-pendent marker for CAA after controlling for relevant con-founding variables. Conclusion: PCT levels can be assessed as a predictor in patients with complicated acute appendicitis which is strongly indicated in patients with PCT levels greater than 0.5ng/ml.