We describe herein the results of (i) enzymatic recognition for imidazopyridopyrimidine (Im):naphthyridine (Na) base pairs and (ii) further primer extension reactions after the Im:Na base pairs by DNA polymerases. Among the base pairs examined, ImN(O):NaO(N) base pair was rather selectively recognized by Klenow fragment exo(-) [F(exo(-))]as complementary base. However, this DNA polymerase did not catalyze primer extension reactions after the ImN(O):NaO(N) base pair. Therefore, we carried out a screening of DNA polymerases to promote the primer extension reaction as well as to improve the selectivity of base pair recognition. As a result, a family B DNA polymerase, especially Deep Vent (exo(-)), seemed most promising for this purpose.