A multi-namespace storage device includes a nonvolatile memory which includes a first memory block and a second memory block different from the first memory block, and a memory controller which receives, from a host, a command for requesting creation of a first namespace including a first logical block number and a second namespace including a second logical page number not included in the first logical block number and receives a physical mapping command for instructing physical mapping of the first namespace. The memory controller performs a first mapping operation by mapping the first logical block number to the first memory block and performs a second mapping operation by mapping the second logical page number to a second memory page included in the second memory block in response to the physical mapping command.