Storage devices including a flash memory and a memory controller, and write memory block allocating methods of the storage devices are provided. A write memory block allocating method may include storing a pre-allocation table in a Random Access Memory (RAM) of a memory controller. The pre-allocation table may include allocation order information of a pre-allocated memory block included in a flash memory. The method may also include receiving a write request from a host, determining whether a write memory block for the write request can be allocated according to the pre-allocation table and allocating the pre-allocated memory block as the write memory block according to the pre-allocation table when the write memory block can be allocated according to the pre-allocation table.