Polymerization catalyst composition, method for producing polymerization catalyst composition, and method for producing conjugated diene polymer

A polymerization catalyst composition comprising:

• a rare earth element carboxylate;
• and
• a phosphate ester represented by the following general formula (1), and
• no organoaluminum compound;
• wherein the polymerization catalyst composition is obtained by a method comprising the following steps (a), (b) and (c):
• a step (a) of adjusting a content of a phosphoric acid ester represented by the general formula (1) within a range of 0.01 to 20 eq relative to the rare earth element contained in the rare earth element carboxylate;
• a step (b) of adjusting a content of water to 0.5 eq or less relative to the rare earth element contained in the rare earth element carboxylate at a reaction temperature of 80 to 160° C.;
• and
• a step (c) of adjusting a total content of free fatty acid and water to 0.6 eq or less relative to the rare earth element contained in the rare earth element carboxylate:
• [Formula 1]
• O═P(OR)3 (1)
• wherein Rs are each independently an alkyl group having 5 to 20 carbon atoms;
• and
• wherein a content of the phosphoric acid ester is 0.01 to 20 eq relative to the rare earth element contained in the rare earth element carboxylate.