A tridecaribonucleotide, r(UGAGCUUCGGCUC) doesn't form hairpin or interior loop and forms a double helix of 12 base pairs including the four successive nonstandard base pairs, U.G-U.C-C.U-G.U, in the crystal. Non-Watson-Crick base pairs, G.U and U.C are nicely incorporated in RNA duplex maintaining the regular A-form backbone. There exist the good overlapping between base pairings, U.G and U.C, so as to stabilize the nonstandard base pair track. Hydrogen bond networks involving water molecules in the major and minor grooves to stabilize this mismatch base pairing array, are observed and its conformational features are described.