Disclosed herein is a self-competitive primer for preferentially amplifying a sample nucleic acid based on whether a selected region thereof has a nucleotide variation, in comparison with a selected region of a reference nucleic acid. The self-competitive primer includes a 5′-competing domain and a 3′-elongating domain. Sequences of the 5′-competing domain and the 3′-elongating domain are complementary to a first region and a second region of the reference nucleic acid, respectively. The first region includes the selected region and at least one nucleotide residue immediately downstream of the selected region of the reference nucleic acid. The second region is located downstream of the selected region of the reference nucleic acid and does not comprise the selected region of the reference nucleic acid, and the first region and the second region overlap by at least one nucleotide. Also disclosed herein is a method for preferentially amplifying a variant sample nucleic acid over a non-variant sample nucleic acid.