The hetero duplex molecule, r(CGCA)d(AAAAAGCG):d(CGCTTTTTTGCG) which corresponds to Okazaki fragment was synthesized and its molecular structure has been analyzed by NMR study. The RNA strand of RNA-DNA hybrid region adopts A-form and DNA strand of the same region deviates from the standard B-form. The conformation of DNA-DNA duplex segment belongs to B-form. The hybrid-DNA duplex junction shows a structural discontinuities, A-B junction. The same conformational characteristic of oligo(dA): oligo(dT) tract as that of DNA oligomer which has same base sequence has been observed.