The present invention provides a composition containing a buffer solution and a single-stranded nucleic acid molecule that comprises a nucleotide sequence represented by 5'-AGCAGAGUACACACAGCAUAUACC-P-GGUAUAUGCUGUGUGUACUCUGCUUC-P-G-3' (SEQ ID NO: 1) (in the sequence, P indicates a proline derivative linker represented by (I) in the specification), wherein the composition is characterized in that (a) the composition is in the form of a solution at normal temperature, and (b) the nucleic acid molecule content after the composition is stored for four weeks at 25°C and 60% RH is 80% or more relative to the nucleic acid molecule content at the start of storage.
