From 7 February until 20 March, customers will have the chance to order a Mac Jr or Grand Mac with their fries when visiting any of the chain's many UK restaurants.
The former is a smaller take of the classic Big Mac, with one all-beef patty instead of two.
And sure to appeal to anyone feeling particularly peckish, the latter is a supersized version of the original.
Served in a soft sesame seed bun with a layer of cheese, the Mac Jr and Grand Mac are both smothered in special sauce. Shredded lettuce and a sprinkling of sliced pickles and diced onion add crunch to the burgers.
Steven Howells, head of marketing at McDonald's UK, is sure customers of the fast food giant will love the new patties.'As an iconic McDonald's product, we are proud and excited to be celebrating 50 years of the legendary Big Mac® and for the first time ever in the UK, introducing the two new sizes for a limited time,' he said.
'We know a lot of our customers will remember the 1974 launch of the Big Mac in the UK and have continued to enjoy the burger and pass the Big Mac® love on since then, it remains our most iconic burger!'
Desperate to get their hands on newest additions on the menu, a number of individuals hit their local McDonald's early this morning.
'Here we go! I was the first to get it in my store! @McDonaldsUK @McDonaldsCorp #grandbigmac,' one hungry burger fan wrote on Twitter alongside a picture of his meal.
Another added: 'Need the #GrandBigMac in my life @McDonaldsUK 🍔🍟.'
First created in the US in 1968 by an American named Jim Delligatti, the Big Mac arrived in the UK back in 1974 when the first restaurant opened on Woolwich High Street.
Are you tempted to try the new limited-edition burgers? Let us know in the comments!