Provided is an internal olefin sulfonate composition which is capable of exerting good foamability together with good volume of foam, foaming speed, foam dissipation property, foam quality, foam durability in the presence of sebum, and volume of foam in the presence of sebum at high levels, and a cleansing composition containing the same. The internal olefin sulfonate composition comprises (A) an internal olefin sulfonate having 16 carbon atoms and/or (B) an internal olefin sulfonate having 18 carbon atoms, in which a total content of the component (A) and the component (B) is from 50 to 100% by mass, a content mass ratio of the component (A) to the component (B), (A/B), is from 91/9 to 100/0, a content of the internal olefin sulfonate in which a sulfonate group is present at a C-2 position is 25% by mass or less, and in which a mass ratio of a content of a hydroxy form in the internal olefin sulfonate of the component (A) and the component (B) to a content of an olefin form in the internal olefin sulfonate of the component (A) and the component (B), (hydroxy form/olefin form), is from 75/25 to 100/0.
