The present report deals with the preparation of crystalline 5'-O-mono-p-metho-xytrityl or 5'-O-trityl derivatives of four common ribonuoleosides [e.i.(MeOTr)Cp,(MeOTr)Up,(MeOTr)Ap,(Tr)Gp^ac]through the direct reaction of the ribonucleoside 3'-phosphate with mono-p-methoxytrityl chloride or trityl chloride.We have found more satisfactory reaction conditions through changing the proportions of reagents,solvents,temperature and the time of reactions.It-should be mentioned that the key point of getting a crystalline trityl-or mono-P-methogytrityl-derivative is to choose an appropriate solvent or mixture of solvents.