A stable 6-methoxy-2', 3'-dideoxyguanosine comprises 6-30% water content. It is prepared by absorbing water in 6-methoxy-2', 3'-dideoxyguanosine with less than 6% water content at low temperature and certain humidity, or drying 6-methoxy-2', 3'-dideoxyguanosine with more than 30% water content. The stable 6-methoxy-2', 3'-dideoxyguanosine can be used to prepare medicament composition, and be used to manufacture pharmaceutical for fighting hepatitis B virus or HIV.
