Abstract: This study investigated the possibility of IgG secreted from tumor cells as a target for radioimmunoimaging and targeted therapy of cancers. Goat anti-human IgG polyclonal antibody (GAHG) was radioiodinated using Iodogen method, and the in vitro stability and pharmacokinetics were evaluated. The biodistribution and γ imaging of 125I-GAHG were performed in nude mice bearing HT-29 human colon cancer xenografts. The 125I-GAHG showed good in vitro stability, and its blood clearance was defined as a two-compartment model, with the T1/2α and T1/2β were 1.19 h and 43.99 h, respectively. The tumor uptake of 125I-GAHG was much higher than that of 125I labeled normal goat IgG control (125I-GIgG). The 125I-GAHG showed good tumor retention when injecting via intra-tumor. In the biodistribution studies，the highest tumor uptake of 125I-GAHG was 6.71± 2.19 %ID/g at 72 h postinjection and the T/NT values increased along with the postinjection time. It suggests that the IgG deriving from tumor cells may provide a novel target or research idea for radioimmunoimaging and targeted therapy of cancers.