The purpose of this study was to investigate the toxicity of hematoporphyrin-coated magnetic ferrofluid (HP-MF) through intravenous administration in Sprague-Dawley rats. Each group was treated with either saline, or the HP-MF at 0.5, 1, 1.5, 2 and 4 ml/kg body weight (b.w.) for the observation of survival rate, clinical symptoms, laboratory values and histopathological findings. In this study, HP-MF was evaluated for the survival rates, symptoms, laboratory values and histopathological examination after treatments. The result revealed that the animals in the group of HP-MF at 2 and 4 ml/kg b.w. showed some lethality. In serum biochemistry, the levels of AST, ALT and ALP were increased in the MF and HP-MF treated groups. However, histopathological examination for the suspected organs showed no evidence of hepatotoxicity and nephrotoxicity of typical iron poisoning. Though the toxicity of HP-MF was higher than that of HP, long retention of hematoporphyrin via HP-MF provides additional benefit over conventional hematoporphyrin. HP-MF could be utilized as a potential photodynamic agent in cancer therapy. It is suggested to develop an efficient external magnetic device to attract hematoporphyrin in the target site, thereby enabling to administering a small amount of HP-MF.