The thermal properties of hydrate-bearing sediments can help to evaluate the stability of hydrate reservoir and improve the safety of natural gas hydrate exploitation. In this work, the thermal conductivities of methane hydrate and methane hydrate-bearing seasand were investigated by the transient plane source (TPS) technique. The high-quality samples of hydrate were prepared by synergistic uses of a variety of methods, i.e., the "seeding" ice, simultaneous slowly heating and slowly supplying gas, temperature oscillation and aging method. The measured thermal conductivity of methane hydrate is 0.4877-0.5467 W.m(-1).K-1 with the temperature 263.2-283.1 K and the pressure 4.0-9.5 MPa. The effective thermal conductivities of the saturated seasand sample, supersaturated seasand sample and unsaturated seasand sample (Here, the "saturated", "unsaturated" and "supersaturated" refers to the three relationships between the pore volume of seasand and the volume of ice powder, respectively) are 1.1310-1.2703 W.m(-1).K-1, 1.0070-1.1490 W.m(-1).K-1, 0.9221-1.1980 W.m(-1).K-1 with the pressure 8.0 MPa and the temperature 253.8-281.2 K, respectively. The effective thermal conductivities of the saturated sample, supersaturated sample and unsaturated sample are 1.1280-1.1402 W.m(-1).K-1 (1.1331-1.5974 W.m(-1).K-1), 1.0172-1.0252 W.m(-1).K-1 (1.0181-1.2032 W.m(-1).K-1), 0.9154-0.9388 W.m(-1).K-1(0.9401-1.1543 W.m(-1).K-1) with the pressure 4.0-10.0 MPa and the temperature 263.2 K (275.2 K), respectively. The relationship between the effective thermal conductivity and methane hydrate saturation in the sample are lambda(e,saturated) > lambda(e,supersaturated) > lambda(e,unsaturated.) The results suggest that the thermal conductivities of methane hydrate and methane hydrate-bearing seasand are positively correlated with the temperature and the influence of the gas phase pressure is negligible. Besides, the effective thermal conductivity shows a sudden increase near to the phase equilibrium temperature. Due to the complex of actual samples, the same classic theory model cannot accurately predict three samples simultaneously. (C) 2019 Elsevier Ltd.