A method for manufacturing a puncture-sealing agent, which effectively prevents gelification of the puncture-sealing agent caused by agglomerates of rubber latex and that can enhance the productivity of the puncture-sealing agent is provided. The manufacturing method includes a first mixing process of mixing an antifreeze liquid with water to obtain a mixture liquid A1; a second mixing process of adding the mixture liquid A1 dropwise into a rubber latex that is being stirred and performing mixing to obtain a mixture liquid A2, while increasing the stirring speed as a liquid amount of the mixture liquid A2 increases; and a third mixing process of mixing the mixture liquid A2 with a tackifier. An amount of variation in the stirring speed is preferably from 0.1 rpm/mm to 6.0 rpm/mm, and a dropwise-addition rate of the mixture liquid A1 is preferably from 0.5 kg/min to 500 kg/min.