A method for producing a polymerization catalyst composition for catalyzing the production of a conjugated diene polymer, comprising: mixing and aging a second element and a third element, and then adding a first element to the mixture to react the first element with the mixture, wherein the first element is a compound that contains a rare earth element (REE-containing compound) wherein the REE-containing compound contains a rare earth element compound (REE compound) or a reactant of the REE compound with a Lewis base, the second element contains a compound represented by the following formula (X): YR 1 a R 2 b R 3 c (X) wherein: Y is a metal selected from Group 1, Group 2, Group 12, and Group 13 of the periodic table; R 1 and R 2 are hydrogen atoms or hydrocarbon groups each having 1 to 10 carbon atoms; and R 3 is a hydrocarbon group having 1 to 10 carbon atoms, R 1 , R 2 , and R 3 are the same as or different from each other, with a being 1 and b and c both being 0 when Y is a metal selected from Group 1 of the periodic table, a and b being 1 and c being 0 when Y is a metal selected from Group 2 and Group 12 of the periodic table, and a , b , and c are all 1 when Y is a metal selected from Group 13 of the periodic table, and the third element contains silica, and the water content of the third element is 0.1 wt% or more. mixing and aging a second element and a third element, and then adding a first element to the mixture to react the first element with the mixture, wherein the first element is a compound that contains a rare earth element (REE-containing compound) wherein the REE-containing compound contains a rare earth element compound (REE compound) or a reactant of the REE compound with a Lewis base, the second element contains a compound represented by the following formula (X): YR 1 a R 2 b R 3 c (X) wherein: Y is a metal selected from Group 1, Group 2, Group 12, and Group 13 of the periodic table; R 1 and R 2 are hydrogen atoms or hydrocarbon groups each having 1 to 10 carbon atoms; and R 3 is a hydrocarbon group having 1 to 10 carbon atoms, R 1 , R 2 , and R 3 are the same as or different from each other, with a being 1 and b and c both being 0 when Y is a metal selected from Group 1 of the periodic table, a and b being 1 and c being 0 when Y is a metal selected from Group 2 and Group 12 of the periodic table, and a , b , and c are all 1 when Y is a metal selected from Group 13 of the periodic table, and the third element contains silica, and the water content of the third element is 0.1 wt% or more. Y is a metal selected from Group 1, Group 2, Group 12, and Group 13 of the periodic table; R 1 and R 2 are hydrogen atoms or hydrocarbon groups each having 1 to 10 carbon atoms; and R 3 is a hydrocarbon group having 1 to 10 carbon atoms, R 1 , R 2 , and R 3 are the same as or different from each other, with a being 1 and b and c both being 0 when Y is a metal selected from Group 1 of the periodic table, a and b being 1 and c being 0 when Y is a metal selected from Group 2 and Group 12 of the periodic table, and a , b , and c are all 1 when Y is a metal selected from Group 13 of the periodic table, and the third element contains silica, and the water content of the third element is 0.1 wt% or more. <EOS>