The absorption spectrum of the hemoglobin (Hb) in single living intact red blood cell (RBC), exposed in 900 MHz radiofrequency electromagnetic wave (RF-EMW), was non-invasive,in situ, real-time measured by employing a highly sensitive fast multi-channel microspectrophotometer system. Both the absorption intensity and site of intracellular Hb were altered after RBCs were exposed in 900 MHz RF-EMW with power density at 5 mW/cm2. It was indicated that not only the concentration of Hb in living RBCs was decreased, but the molecular structure of Hb was changed by the RF-EMW action.