The present invention provides a surfactant composition which includes 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 the component A; C: a nonionic surfactant; D: water.