Raman titration experiment with magnesium salt added gradually to aqueous solution of duplexes formed by RNA homopolynucleotides polyU and polyA was performed to reveal its effect on homopolynucleotide complexes. Statistical analysis of obtained spectral set has confirmed the effect already found by less structurally sensitive methods [Nucleic Acids Res. 31(17) (2003), 5101–5107] that at sufficiently high concentrations magnesium causes transformation of polyU·polyA duplexes to polyU·polyA·polyU triplexes and single polyA strands. It was found that at relatively high polynucleotide concentrations used in Raman experiment, the threshold magnesium concentration for this effect is above the concentration of duplex basepairs in solution. Due to the strong spectral changes attributed to the varied percentages of duplexes, triplexes and single strands, it was not possible to register weaker direct Raman signs of the magnesium binding to polynucleotide strand.