Aipysurus tenuis, also known as the Arafura sea snake, Mjoberg's sea snake, or brown-lined sea snake, is a species of venomous snake in the family Elapidae that is native to Australia. The specific epithet tenuis ("slender") refers to the snake's appearance.
The species grows to an average of about 130 cm in length. It is long and slim, with a small, brown head and a pale body.
The species is viviparous.
The snake is found in marine waters off the north-west coast of Western Australia, from near Dampier to Broome, and in the Arafura Sea. The type locality is Cape Jaubert, near Broome.