The evaluation of the Gd-carborane complex 2 as an MR imaging and boron carrier agent was carried out in vivo using tumor-bearing Donryu rats, MRI, ICP-AES, and alpha-autoradiography. The MR imaging revealed that the carborane Gd-DTPA 2 was metabolized slower in the body than Gd-DTPA 1. The results of the ICP-AES method indicated that compound 2 was incorporated into normal tissues and metabolized quickly, whereas it was not accumulated into tumor or brain tissue. The alpha-autoradiography showed that a high level of boron was obtained in the internal organs and in the necrosis of tumor tissue.