A new class of phosphorylated nucleosides, i.e., adenosine 6-N-phosphoramidate (6-N-AMP) and related derivatives, were synthesized in good yields via phosphitylation of the amino group of appropriately protected adenosine derivatives. In a similar manner, cytidine 4-N-phosphoramidate (4-N-CMP), guanosine 2-N-phosphoramidate (2-N-GMP), and their diethyl ester derivatives were synthesized. These new compounds were characterized by H-1, C-13, and P-31 NMR, UV, CD, IR, electrophoresis, and mass spectroscopy. The physical and chemical properties of these N-phosphorylated ribonucleoside derivatives have been studied in detail.