Abstract: Mammalian olfactory system can accurately identify odorants with high specificity and sensitivity. Taking advantage of multiple microelectrode implant technology, we developed a novel in vivo biosensing system for odor detection. The odorant information from conscious rats' olfactory bulb (OB) is extracted by using microelectrode array. High-quality mitral/tufted (M/T) cell activity evoked by odorants could be obtained for at least three weeks. The responses of M/T cell carry sufficient information to discriminate presented odorants. In addition, we found the concentration detection limit of rat is below 10-10 mol/L for carvone. These results demonstrate that in vivo biosensing system has the characteristics of high sensitivity, continuous recording, and specificity, which presents a promising platform for specific trace odorant detection in many fields.