S Orionis is an asymptotic giant branch star in the constellation Orion, approximately 480 parsecs (1,600 ly) away.

S Orionis is a Mira variable that pulsates with an approximately 420‑day cycle, and varies in radius from 2.0 to 2.3 astronomical units.

The variations are approximately sinusoidal with a weak, not statistically-significant, trend towards longer period.

However, this behaviour is not expected to be the result of thermal pulses or evolutionary changes, and the cause is unknown.

[8] S Orionis is surrounded by masers and dust condensed from its cool stellar wind.