VX Sagittarii is an asymptotic giant branch star located more than 1.5 kiloparsec away from the Sun in the constellation of Sagittarius.

The spectral type varies between M4e around visual maximum and M9.8e at minimum light, and the luminosity class is Ia indicating a bright supergiant.

The spectrum shows emission lines indicating that the star is losing mass through a strong stellar wind.

[7][8] Its atmosphere is extended, irregular, and variable during the pulsations of the star, but the bolometric luminosity varies less than the visual brightness and is calculated to be about 195,000 L☉.

In many respects the atmosphere is similar to low mass AGB stars such as Mira variables, but with a supergiant's luminosity and size.