Provided is a protected nucleotide for elongation that makes it possible to realize a method for producing oligonucleotides by the phosphoramidite process that allows purification to be conducted by liquid-liquid extraction efficiently and at high yield. It was discovered that this can be achieved by using a specific base-protected oligonucleotide and/or a specific aromatic protected oligonucleotide containing a 3'-position branched chain.
