The 48-year-old actor revealed the poster late last night on his Twitter account.
In the first look, Aamir is seen walking nude on a railway track with a huge radio protecting his modesty.
"What do you think guys Tell me fast... Butterflies in my stomach!," Aamir tweeted.
The 'Dhoom 3' star, who is known for experimenting his looks in the film, appeared nude for the the first time in his more than three-decade-old career.
This is the the second time that the Bollywood's perfectionist is teaming up with Hirani after the stupendous success of '3 Idiots'.
Image courtesy: Bollywoodhungama.com
'PK', a satire on godmen, also stars Anushka Sharma and Sushant Singh Rajput in prominent roles. It is expected to hit theatres on December 19.