An indole group in an amino acid or a peptide can be protected with a group shown by the formula: ##STR1## wherein R.sub.1 and R.sub.5 each is hydrogen, methyl or methoxy; R.sub.2 and R.sub.4 each is hydrogen or methyl; and R.sub.3 is methyl or methoxy, and said group may easily be removed without affecting the amino acid or the peptide to be derived from the protected amino acid or peptide. Thus, the present invention is useful in the synthesis of a peptide containing an indole group.