Objective To evaluate the effect of near infrared heptamethine cyanine dye IR-783-mediated specific tumor imaging in spontaneous tumor of dogs. Methods IR-783 was intraperitoneally injected to nude mice models of transplanted tumor in a dose of 5μmol/kg. The metabolic time course of IR-783 was detected by in vivo imager. Based on the results of above observation, IR-783 was injected to dogs with spontaneous tumor in a dose of 1.5μmol/kg. The site of intravenous injection was the hind leg. Tumor and peri-tumoral tissues were removed at 5 days after IR-783-injection for fluorescence imaging, pathology and frozen section fluorescence examinations. Results After i.p. IR-783 injection to nude mice models of transplanted tumor, the transplanted tumor tissues of nude mice had stronger specific fluorescence than normal tissues by imaging at 8 days after injection. After i.v. IR-783 injection to four dogs with spontaneous tumor, the fluorescence signal in the tumor tissues was stronger than that in the normal tissues at 5 days after injection. Conclusions Near infrared fluorescent dye IR-783 could be specifically taken up by tumor tissues, and can be used for specific diagnosis of tumor. It has an important clinical application prospect.