U Orionis (abbreviated U Ori) is a Mira-type variable star in the constellation Orion.

It is a classical long period variable star that has been well observed for over 120 years.

Thus U Orionis became the first long period variable to be identified by a photograph of its spectrum.

The star has a low effective temperature (variable with the pulsations, but roughly 2,700 K), a large and bloated radius of 370 R☉,[5] and a high luminosity, 7,000 times higher than the Sun.

[6] If the Sun were replaced with U Orionis, its radius would extend beyond Mars's orbital zone (about 1.7 astronomical units).