The effect of bulk density and moisture content on the thermal conductivity of some Jordanian soils was investigated through laboratory studies. The soils used were classified as sand, sandy loam, loam, and clay loam. The hot wire method was used to perform the experiments. Heating and cooling methods were used to evaluate thermal conductivity for the soil types and the results obtained by the two methods were compared. Thermal conductivity increased with increasing soil density and moisture content. It was found that the soil containing higher percentage of clay particles had lower thermal conductivity. Graphical comparisons of thermal conductivity obtained by both methods, cooling and heating, for each soil type are presented. In general, the heating data yielded thermal conductivities that were slightly higher than those derived from the cooling data. (C) 2001 Elsevier Science Ltd. All rights reserved.