A novel phosphotriesterified ribonucleic acid compound which is important for liquid-phase synthesis of oligo-RNA is provided. Examples of the ribonucleic acid compound of the invention may include ribonucleic acid compounds represented by the following general formula: (wherein B represents adenine, guanine, cytosine or uracil or a modified form thereof; R21 represents aryl which may be substituted or a monocyclic or bicyclic heterocyclic group which may be substituted; R20 represents H or alkyl which may be substituted; and R1 represents a protecting group which can be removed at 90% or more at a temperature in the range from 0° C. to 60° C. under acidic conditions at a pH value from 2 to 4 within 24 hours).