A polymerization method in which a first liquid and a second liquid are mixed in a gas phase and polymerized in the form of droplets is disclosed, wherein a polymerizable monomer and a polymerization initiator are each contained in at least one of the first liquid and the second liquid, and at least one of the first liquid and the second liquid is injected in a spatially expanding film shape. By employing the polymerization method of this invention, high-quality polymer can be efficiently produced in large quantity by the droplet polymerization even using a polymerizable monomer with a rapid reaction rate.