The present invention provides a surfactant composition which contains a surfactant at a high concentration, while having fluidity over a wide concentration range. A surfactant composition according to the present invention contains the components A, B, C and D described below, and is configured such that: the total content of the components A, B and C is from 30% by mass to 80% by mass (inclusive)； the mass ratio of the total content of the components A and B to the content of the component C, namely (A + B)/C is from 20/80 to 80/20； and the mass ratio of the content of the component A to the content of the component B, namely A/B is from 98/2 to 45/55. A: an internal olefin sulfonic acid and/or a salt thereof B: an anionic surfactant other than component A C: a nonionic surfactant D: water.本發明提供一種界面活性劑組合物，其以高濃度含有界面活性劑，且於較廣之濃度區域具有流動性。本發明之界面活性劑組合物含有下述成分A、B、C及D， 成分A、B及C之合計含量為30質量%以上且80質量%以下， 成分A及B之合計含量與成分C之含量之質量比(A+B)/C為20/80~80/20，且 成分A之含量與成分B之含量之質量比A/B為98/2~45/55。 A 內部烯烴磺酸及/或其鹽 B 成分A以外之陰離子界面活性劑 C 非離子界面活性劑 D 水
