Purine nucleosides which are fluorinated at the 3'-position (preferably the .alpha.-position), may be economically and efficiently produced by fluorinating a novel purine nucleoside derivative (1) in which the hydroxyl group at the 5'-position is protected to obtain a novel purine nucleoside derivative (2) in a high yield. The derivative (2) is subjected to desulfurization, deprotection of R.sup.1 and, as necessary protection, deprotection, or modification of nucleic acid base moiety, to obtain the desired purine nucleoside (3). wherein each symbol is as defined in the specification.