We studied basic physical and chemical properties of archaeological wood buried in the soil or preserved underwater in the Ljubljana Moor, Slovenia. The wood of oak (Quercus sp.), ash (Fraxinus sp.), alder (Alnus glutinosa), beech (Fagus sylvatica), and maple (Acer sp.) was selected from vertical pilesfrom 5 prehistoric pile dwellings from the 3rd and from the 4th millennium BC. Moisture content above 500% and a drastic decrease in basic density indicated a very high degree of wood deterioration. Shrinkage was much higher than that in recent wood. Chemical analyses of ashwood have shown adrastically increased amount of lignin and a reduced amount of cellulose and hemicelluloses. The results present basic knowledge for future planning of proper conservation treatment of the wood used in dendrochronological investigations.