A multilevel cell (MLC) nonvolatile memory system including a plurality of memory cells each cell storing first bit data and second bit data, and a controller programming the plurality of memory cells on a page-by-page basis, the controller programming original data to an original block and programming copy data that is the same as the original data to a mirroring block, wherein first bit page data and second bit page data of the original data are programmed to memory cells connected to the same word line, but the first bit page data and second bit page data of the copy data are programmed to memory cells connected to different word lines.