Her huge diamond was hard to miss as she appeared in an affectionate display with her fiance Theroux in Santa Fe at the weekend, enjoying a break in the New Mexico region, reported Daily Mail.
Aniston is taking a hiatus from her latest project, "We're the Millers", which has been filming in Albuquerque.
As the pair left their accommodation, the blonde bombshell, 43, flaunted her huge jewellery piece as she caressed her partner's face, prompting him to smile.
The stone glimmered as she stroked Theroux's arm.
The actor donned black jeans, biker boots and scarf with cool aviator shades.
The couple announced their engagement in August after Theroux popped the question on his 41st birthday.
Aniston was spotted wearing a thin gold band shortly after, but this is the first sighting of the huge diamond.
Meanwhile, the pair are reported to have chosen their holiday destination as their wedding location.