Daniel Otto Christian Isaachsen (22 August 1806 – 9 December 1891) was a Norwegian businessperson and politician.
He was born in 1806 as the son of wealthy businessman Daniel Isaachsen and his second wife Hanne Susanne Nideros.
He married a Laura Pedersen.
He was the half-brother of Peder and Isaach Isaachsen.He was elected to the Norwegian Parliament in 1839, representing the constituency of Christianssand.