The effect of 5'-phosphorylation at nicks on DNA stabilization was measured through the formation of DNA multiassemblies consisting of 40-mer half-sliding complementary oligon-cleotides, which had overlapping complementary 20-mer base sequences. 5'-Phosphorylated oligonucleotides formed longer DNA multiassemblies than 5'-hydroxylated ones. This result indicated that the 5'-phosphorylated sticky ends contribute to the stabilization of the DNA association due to the hydrogen bonds between 3'-hydroxy groups and 5'-phosphate groups at the nick positions.