Background: This study aimed to determine the value of the ESR, CRP and Leukocyte count in the diagnosis of acute appendicitis.Materials and Methods: This is a retrospective (descriptive-analytic) study which was conducted from August 2007 until October 2008 in Zahedan. A sample of 426 available patients with suspected acute appendicitis –who had been admitted to Ali-ebne- Abitalib and Khatam-al-Anbia hospitals– were recruited to participate in this study. Patients’ demographic data, their blood samples for ESR, CPR and Leukocyte count were collected and sent to the laboratory for analysis. SPSS-16 was used to analyze data.Results: A number of 426 patients were investigated. Nearly 59.9% were male and 81% of the patients had leukocytosis.214 cases of inflamed papillae (50.4%), 102 cases of exudation (23.9%), 36 cases of gangrene (8.5%) and 25 cases of perforated appendicitis were observed during the operations. Seven cases had abscess or flegmon. Pathological reports of 84 patients (19.7) showed normal appendices. Sensitivity and specificity value of ESR and CRP tests were (71.9 & 39.0%) and (85.0% & 57.0%) respectively. Positive and negative predictive value (PPV and NPV) of both tests were 83, 25, 89, and 48% respectively. ESR and CRP and leukocytosis had significant statistical correlation with phonological results.Conclusion: The results of this study showed that in addition to physical examination, some basic laboratory findings such as ESR, CPR and leukocytosis can be helpful. Among these, the value of CPR in the diagnosis of acute appendicitis is higher.