Abstract: The image state of the testis of Fischer344 rats were observed by SPECT with 99^m TC-FDX (molecular weight: 48000). Rats were injected at the dose of 0.1ml (18.5MBq) through the tail vein. Testicular tissues for examination were fixed in 10% neutral buffered formalin, embedded in paraffin, and stained with iron - hematoxylin and H. E. The results showed that the testicular tumor of the rats were imaged positively, and pathological findings further confirmed that it belonged to the interstitial cell tumor. The Reinke crystalloids have been observed in the cytoplasm with the iron-hematoxylin. The results suggest that the 99^m TC-FDX and staining with iron-hematoxylin is an ideal method for the early diagnosis of testicular interstitial cell tumor.