An object of the present invention is to provide a process capable of producing a self-assembling peptide derivative that is useful in the fields of regenerative medicine and surgery in large quantities and in an economical and efficient manner. In particular, provided is a production process employing a combination of (i) a step of convergently constructing a sequence with use of a common repeating unit consisting of a specific amino acid sequence and (ii) a step of first isolating the peptide derivative as a disulfuric acid salt, a tetramethanesulfonic acid salt or a tetra(trifluoroacetic acid (TFA) salt), and then subjecting the peptide salt to a salt exchange reaction to yield a tetrahydrochloric acid salt.