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 of the present invention comprises (A) an internal olefin sulfonate having 16 carbon atoms and (B) an internal olefin sulfonate having 18 carbon atoms, wherein a mass content ratio (A/B) of component (A) to component (B) is from 75/25 to 90/10, and wherein a mass ratio (hydroxy form/olefin form) 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) is from 75/25 to 100/0.