Novel phosphorsulfide derivatives of deoxynucleosides or deoxynucleotides are provided, which have the general formula: ##STR1## wherein R.sup.1 is a hydroxy-protecting group; R.sup.2 is a phosphate-protecting group; R.sup.3 is an aryl group; B.sub.1 and B.sub.2 may be the same or different and each are a base residue which may have a protecting group; and n is zero or a positive integer, provided that if n is 2 or larger, the respective R.sup.2 may be the same or different. They are prepared by reacting a deoxynucleoside or deoxynucleotide with a 1,2,4-triazolylphosphine compound and are useful as intermediates for the preparation of oligodeoxy-nucleotides.