CoSb3 micrometer powder was synthesized by solidstate reaction using high pu rity powder of Co,Sb as the starting materials.CoSb3 nano-powder was prepared by highenergy ballmilling.CoSb3 block material with the average grain size of 150nm was prepared by Spard Plasma Sintering(SPS).The influence of nanostru cture on thermal transport properties of CoSb3 was investigated systematicall y .When the grain size of CoSb3 decreases from micrometer to namometer,the lattice thermal conductivityκL of compounds falls remarkably,while the carries thermal conductivity κc decreased less drastically than did the lattice thermal conductivity κL.The decrease in thermal conductivity of CoSb3 compounds with decreasing grain size was mainly due to the reduction in lattice thermal conductivity.