In the title compound, C16H21NO2, the indoline ring and the two ketone O atoms are approximately coplanar, the largest deviation from the mean plane being 0.063 (2) Å. The mean plane through the fused ring system is nearly perpendicular to the mean plane passing through the 1-octyl chain [dihedral angle = 77.53 (17)°]. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds, forming a three-dimensional network.