The present invention provides a method for producing a high-quality internal olefin sulfonate in which the content of any internal olefin and inorganic substance is small. This method for producing an internal olefin sulfonate, comprising: a sulfonating step of causing an internal olefin to react with sulfur trioxide to yield a sulfonated internal olefin; a neutralizing step of mixing the resultant sulfonated internal olefin with an aqueous alkaline solution at 40° C. or lower to yield a mixture, and applying shearing force to the mixture until the particle diameter of oil droplets of an oily product of the mixture turns to 10 μm or less to yield a neutralized product; and a hydrolyzing step of hydrolyzing the resultant neutralized product.