A method of programming a non-volatile memory device including a first memory block and a second memory block includes: performing a first program operation on a first memory cell in the first memory block and connected to a first word line of a first level with respect to a substrate; after the performing of the first program operation on the first memory cell, performing the first program operation on a second memory cell in the second memory block and connected to a second word line of the first level; and after the performing of the first program operation on the second memory cell, performing a second program operation on the first memory cell.