{Problems} To provide an agent that is used for searching protein crystallization conditions, and has improved properties of promoting protein crystal formation and improved operability, and a method for searching for protein crystallization conditions using the same. {Means to solve} An agent for searching for protein crystallization conditions, containing a water-swellable layered silicate having a fluorine atom and a hydroxyl group, wherein the fluorine atom is covalently bonded to the silicate by isomorphous substitution with the hydroxyl group. A method of searching for protein crystallization conditions, which comprises a step of mixing the agent for searching for protein crystallization conditions described above and a solution in which a protein is dissolved.
