The objective of this work was to develop an appropriate measurement system to collect accurate data and obtain thermal conductivity values for some fruits and vegetables and for temperatures below the freezing point, since there is limited information available, particularly for vegetables such as spinach, for which the values obtained experimentally are dissimilar to those predicted from composition. The effects of various experimental conditions were also considered, to optimize the line heat source technique used for the measurements. Fresh and frozen strawberry (Tioga variety) and spinach samples as well as blanched spinach were rested in the temperature range from -21 to +28 degrees C. The differences between the thermal conductivity values obtained for a specified temperature range and those cited in the literature showed that the data acquisition system was good and the line heat source technique worked satisfactorily.