Potassium channels are widely expressed in eukaryotic and prokaryotic cells where one of their key functions is to set the membrane potential. Many potassium channels are tetramers that share common architectural properties. The crystal structure of bacterial and mammalian potassium channels has been resolved and provides the basis for modeling their three-dimensional structure in different functional states. This wealth of information on potassium channel structure contrasts with the difficulties to visualize single potassium channel proteins in their physiological environment. We describe a method to identify single calcium activated potassium channel molecules (hIK1) in the plasma membrane of migrating cells. Our method is based on dual-colour labeling with quantum dots (QD). We show that more than 90 % of the observed QDs correspond to single potassium channel proteins. We anticipate that our method can be adopted to label any other ion channel in the plasma membrane on the single molecule level.