Abstract：The olfactory system is important for our quality of life. Humans and other mammals can detect a vast number and variety of environmental chemicals. How does the olfactory system work? To address this question, two American scientists began their research with genes coding olfactory receptor and found the receptors. Moreover, they uncovered the organization of the olfactory system. In 2004, the Nobel Assembly at Karolinska Institute has awarded them the Nobel Prize in Physiology or Medicine for their outstanding contributions. It was introduced in detail how they uncovered this big problem.