PROBLEM TO BE SOLVED: To provide a manufacturing method of high molecular weight polyisobutylene emulsion excellent in stability.SOLUTION: The manufacturing method of polyisobutylene is a manufacturing method of an O/W type polyisobutylene emulsion containing polyisobutylene (A), an emulsifier (B) and water (C) and having a solid content concentration of 1 to 75 mass%, including a mixing process of heating and mixing a mixture by mixing the polyisobutylene (A) and the emulsifier (B), an inversion process of phase inversion from a W/O type emulsion to an O/W type emulsion by gradually adding the water (C) to the heated and mixed mixture of the polyisobutylene (A) and the emulsifier (B) in the mixing process, and the emulsifier (B) is 2 or more mixtures.
