Twoallbeefpattiesspecialsaucelettucecheesepicklesonionsonasesameseedbun is a trademarked slogan used by McDonald's in 1975. The phrase is a somewhat non-sensical word made up by the company, a compound of the words "Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun", which is the ingredient listing for its Big Mac sandwiches.

In 2003, the phrase was revived, both in advertising and liscensed product. In an English-language ad for McDonald's international "I'm Lovin' It campaign that used hip-hop music, a rapper rapidly spouts off the trademark, in the background of the song. Also that year, American Greetings and Carlton Cards released a Christmas ornament of a Big Mac, on which the phrase twoallbeefpattiesspecialsaucelettucecheesepicklesonionsonasesameseedbun was printed.

The word is 71 characters long; had it been real, and not made up for corporate promotion, it could easily qualify to be one of the longest, non-scientific words in the English language.