Objective. The aim of this study was to examine the thermal conductivity of five different root canal sealers in vitro. Materials and methods. Sealapex, AH Plus, AH 26, Endomethasone and RoekoSeal root canal sealers were examined. These materials were prepared in accordance with the manufacturer's instructions and applied to standard molds. Three samples of each material were prepared. The samples were kept for 5 days under 37 degrees C conditions. Measurements were taken using a heat conduction unit (P. A. Hilton Ltd. Stockbridge, Hants, UK). The thermal conductivity coefficient was calculated for each sample using the Fourier equation. Coefficients were analyzed statistically by the Kruskal-Wallis test. Results. Significant differences were found for thermal conductivity between some materials (p < 0.05). The conductivity coefficient of AH Plus was found to be higher than those of the other materials (p < 0.05). No statistically significant differences were found between AH 26 and RoekoSeal (p > 0.05) and the conductivity coefficients of these sealers were found to be lower than those of the other materials (p < 0.05). No statistically significant differences were found between Sealapex and Endomethasone (p > 0.05) and the conductivity coefficients of these sealers were found to be lower than that of AH Plus but higher than those of RoekoSeal and AH26 (p < 0.05). Conclusions. The results showed that root canal sealers functioned as thermal insulators and had different heat-conductive properties that depended on their composition.