THE INVENTION RELATES TO A METHOD FOR PREPARING MORPHINE-6-GLUCURONIDE OR ONE OF THE DERIVATIVES THEREOF, COMPRISING THE FOLLOWING STEPS: (I) REACTING A COMPOUND HAVING FORMULA (I), WHEREIN R1 REPRESENTS A CARBONYL GROUP, COR5CO OR S02R6S02 WITH A GLUCURONIC ACID DERIVATIVE HAVING FORMULA (II) WHEREIN PG REPRESENTS AN ACETYL, ISOBUTYRYL, BENZOYL OR PIVALOYL GROUP, X REPRESENTS A TRIHALOGENOACETAMIDATE GROUP AND R4 REPRESENTS A (C1 –C4)ALKYLCARBOXYLATE GROUP,IN THE PRESENCE OF AN AROMATIC SOLVENT AND TRIFLUOROMETHANESULFONYL OF TRIMETHYLSILANE； (II) REACTING THE PRODUCT OBTAINED IN STEP (I) WITH A STRONG BASIC AGENT； AND, SUBSEQUENTLY, (III) RECOVERING THE PRODUCT OBTAINED IN STEP (II).
