Scarlett Johansson and her fiancé Romain Dauriac, sat opposite Chris Hemsworth and Elsa Pataky
While most of the group are looking at the camera, Samuel appears to be a little distracted by his mobile phone.
It's not the first time that Robert has shared a photo from the upcoming Avengers movie.
The star, who only joined Twitter on 11 April, delighted fans when he posted the first picture from the set of the film on 22 April.
Robert Downey Jr. shared the first photo from the Avengers 2 set earlier this month
"You asked for it! My first tweet from the set of Avengers: Age of Ultron with exec producer @jlatcham," he wrote alongside a picture of the pair posing in high-visibility jackets.
He later shared another photo of the cast’s personalised chairs, writing, "Lights, camera, assemble @MarkRuffalo @Chris Evans."
Avengers: Age of Ultron features a star-studded ensemble cast that includes Robert, Chris Hemsworth, Mark Ruffalo, Chris Evans, Scarlett Johansson, Jeremy Renner, Samuel L. Jackson, Aaron Taylor-Johnson and Elizabeth Olsen.
Robert Downey Jr. also shared this funny photo of the cast's personalised chairs
Robert recently spoke to Variety about the "very ambitious" sequel. "If you read it, it's dense, it's smart. Joss (Whedon) is a really smart guy," he said.
"My two-year-old is crazy about Hawkeye and I think Jeremy (Renner) has a lot to do with the plot. There's always so many plates to spin to get these things half-right, and I'm really excited about this one."