The thermal conductivities of materials (km) are important in many fields such as agriculture, mining and biomedical engineering. For example, better knowing the km values of biomaterials can be useful in radiofrequency ablation (RFA) to treat and/or cure tumor and cancer cells (Liu et al. ). Thermal conductivity probes (TCPs) have proven to be very attractive in obtaining relatively accurate kkm values due to their inline measurements, inexpensiveness, portability, and versatility.However, due to the vast number of designs and applications of TCPs, sources of errors with using the probes are diverse. As a result, in this thesis, possible sources of errors in TCPs (single needle) were investigated. The sources include probe sizes, heating powers, sampling media, selection of TCP materials, location of the thermocouple, axial heat conduction, thermal contact resistance, initiating time t0, decision to use heating or cooling period for km calculations and tolerance in the thermal properties of epoxy.