C‐phycocyanin (C‐PC) was isolated from blue‐green algaspirulinaplatensis. A scanning tunneling microscope (STM) has been used to investigate its three‐dimensional structure. The samples were dialyzed before the STM experiment, and then deposited on highly oriented pyrolytic graphite (HOPG). The measurement was carried out in ambient condition at room temperature. STM images showed thatC‐phycocyanin was uniformly distributed on solid‐state substrate HOPG. The shape ofC‐phycocyanin is disklike with a channel in the center. It is concluded that STM has great potential to observe the structure of biliproteins and phycobilisomes.