A storage device includes a nonvolatile memory including a plurality of nonvolatile memory cells, a write buffer memory storing first data and second data received from a host, and a storage controller storing the first data and the second data that are stored in the write buffer memory into the nonvolatile memory. The storage controller performs a first program operation and a second program operation on a plurality of first memory cells connected to a first word line group to store the first data, and performs a first program operation and a second program operation on a plurality of second memory cells connected to a second word line group to store the second data. While the storage controller performs the first program operation on the plurality of second memory cells, the first data is written in the write buffer memory.