Background and Objective: Histopathological evaluation of granulosa cell tumors (GCT) of the ovary may be confused morphologically with a wide variety of the tumors. Immunohistochemical staining for inhibin and calretinin can be used for better diagnosis. Although it has been suggested that inhibin can be a sensitive marker for GCT, it maybe had negative results in some cases. In addition, caltrinin has been proposed as a marker for GCT. The aim of this study was to investigate the immunohistochemical methods (IHC) including a comparison of calretinin and inhibin markers in the diagnosis of these tumors. Patients and Methods: This prospective study carried out from 2000 to 2009 at Ghaem and Omid hospitals, Mashad University of Medical Sciences, Iran. A total of 23 ovarian GCT specimens were immunostained with commercially available antibodies to find out calretinin and inhibin immunoreactivity. Data were analyzed by descriptive statistical method. A P value of =Results: For diagnosing GCT, the sensitivity of calretinin was 100% and that of the inhibin was almost 73.9%. The extent and severity of staining was more extensive for calretinin compared to inhibin PConclusion: Calretinin is a more sensitive biomarker for GCT than inhibin.