Lymph-node detection system using a high Tc SQUID and ultra-small particles was proposed. Pseudo lymph nodes containing small iron particles were made and the magnetic signal was measured. The SQUID signal was proportional to the weight of the iron in the fluid. At the distance of 20 mm, the detectable minimum weight of the iron was 40 µg. We demonstrated that the possibility of the application of the system to the human body.