Hydrochloric acid leaching of Co, Ni, Cu, Mn and Fe from the cobalt-rich ferromanganese crust under reducing conditions was performed using hydrogen peroxide and sodium sulfite as reducing agents. Hydrochloric acid concentration more than 3.0 mol/dm3 is required to obtain the high extraction of Co and Ni without reducing agents at ambient temperature. The high extraction of Cu in dilute hydrochloric acid solution without reducing agents at ammbient temperature explains the different form of Cu from other metals present in cobalt-rich ferromanganese crusts. When hydrogen peroxide or sodium sulfite was used as reducing agent, the high extraction of Co and Ni was obtained with dilute hydrochloric acid at ambient temperature. In particular, hydrogen peroxide extracts metals in stoichiometric amounts. The extraction of Ni depends significantly on the leaching temperature, regardless of the presence or absence of reducing agents.