This invention provides a rosin-based molecular crystal formed from the following component A and component B: Component A: dehydroabietic acid or a rosin-based resin acid containing dehydroabietic acid as an essential constituent Component B: at least one rosin-based resin acid alkali metal salt selected from the class consisting of lithium, sodium and potassium salts of said component A, a polyolefin resin nucleating agent comprising the rosin-based molecular crystal, a polyolefin resin composition comprising the nucleating agent and if desired a calcium compound, and a molded article obtainable by molding the resin composition.
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