A method for producing lithium-lanthanum-titanium oxide sintered material, the lithium-lanthanum-titanium oxide sintered material is described by chemical formula La 0.57 Li 0.29 TiO 3, amount of Al contained is 0.35 mass% or less as Al 2 O 3, amount of Si contained is 0.1 mass% or less as SiO 2, and average particle diameter measured based on an image obtained by a scanning electron microscope is 21 μm or more, the method comprising steps of: a primary pulverizing step in which lithium raw material in an excess amount of 0 to 15 mass% of the lithium raw material, titanium raw material and lanthanum raw material are mixed and pulverized for 20 to 50 minutes in mixed solvent of pure water and alcohol using an urethane lining ball mill, a nylon ball mill, or a natural rubber lining ball mill as the pulverizing device and a zirconia medium or alumina medium as the pulverizing medium, a resting step in which the raw material is allowed to rest for 10 to 20 hours, and then pulverization is performed again for 20 to 50 minutes, then the primary pulverized raw material is dried and baked at 1000 to 1200 °C under an atmosphere of oxygen, air, or inert gas for 1 to 12 hours, a secondary pulverizing step in which the raw material is pulverized again for 1 to 6 hours with adding mixed solvent of pure water and alcohol and using an urethane lining ball mill, nylon ball mill, or natural rubber lining ball mill as the pulverizing device, then the secondary pulverized raw material is dried in the same manner as the primary pulverized material, and processed in a desired shape by a forming method, and a sintering step in which primary sintering is performed at 1000 to 1200 °C for 1 to 4 hours and secondary sintering is performed at 1200 to 1500°C for 4 to 10 hours, wherein the sintering atmosphere of the primary sintering and the secondary sintering is oxygen, air or inert gas. a primary pulverizing step in which lithium raw material in an excess amount of 0 to 15 mass% of the lithium raw material, titanium raw material and lanthanum raw material are mixed and pulverized for 20 to 50 minutes in mixed solvent of pure water and alcohol using an urethane lining ball mill, a nylon ball mill, or a natural rubber lining ball mill as the pulverizing device and a zirconia medium or alumina medium as the pulverizing medium, a resting step in which the raw material is allowed to rest for 10 to 20 hours, and then pulverization is performed again for 20 to 50 minutes, then the primary pulverized raw material is dried and baked at 1000 to 1200 °C under an atmosphere of oxygen, air, or inert gas for 1 to 12 hours, a secondary pulverizing step in which the raw material is pulverized again for 1 to 6 hours with adding mixed solvent of pure water and alcohol and using an urethane lining ball mill, nylon ball mill, or natural rubber lining ball mill as the pulverizing device, then the secondary pulverized raw material is dried in the same manner as the primary pulverized material, and processed in a desired shape by a forming method, and a sintering step in which primary sintering is performed at 1000 to 1200 °C for 1 to 4 hours and secondary sintering is performed at 1200 to 1500°C for 4 to 10 hours, wherein the sintering atmosphere of the primary sintering and the secondary sintering is oxygen, air or inert gas.