A conservation method using sucrose and mannitol in the impregnation solution has been developed as a new, simple, and effective method for the preservation of waterlogged wood in various states of degradation. The sucrose-mannitol treatment makes it possible to conserve such wood in a one-step process. The method was tested using various waterlogged wood samples from Japan. The concentration of the impregnation solution was increased gradually in four steps. First mannitol, then sucrose was added. The impregnation was concluded at 80°C. The method solved the problems of earlier mannitol treatments, such as whitening of the surface of the treated wood and insufficient consolidation. The sucrose-mannitol mixture gives high stabilization. Antishrink efficiency values were generally over 90% for a wide range of wood quality; maximum water content was 226-668%.