A process for producing a functional molecule includes a forming step which forms a modified nucleotide n-mer (where, n represents an integer) containing a modified nucleoside prepared by introducing a substituent into a nucleoside composing a nucleic acid; and a producing step which produces a modified oligonucleotide sequence by randomly polymerizing the modified nucleotide n-mer. A preferable embodiment thereof includes a selecting step which selects a sequence having an affinity to a target from the modified oligonucleotide sequence, a determining step which amplifies the selected modified oligonucleotide sequence and determines the base sequence thereof, and a translating step which translates the sequence of the modified oligonucleotide sequence on the basis of a relation table prepared by relating at least one of 4.sup.n kinds of nucleotide n-mers, which are presented in the relation table prepared by the one-to-one combination of 4 kinds of nucleosides, to a modified nucleotide n-mer.