The acquisition is the biggest for Oracle since buying Sun Microsystems in a deal announced in 2009 and closed in 2010.
The all-cash takeover comes from Oracle's USD 39 billion cash stockpile and comes after the software giant founded by Larry Ellison produced disappointing results over the past quarter.
"Oracle has successfully helped customers across multiple industries, harness the power of cloud, mobile, social, big data and the Internet of things to transform their businesses," said Oracle's president Mark Hurd.
"We anticipate delivering compelling advantages to companies within the hospitality and retail industries with the acquisition of Micros."
Micros has some 5,67,000 customers, including hotels, casinos, restaurants, retail, leisure and entertainment providers in more than 180 countries.
Its products include so-called point of sale devices -- which replace cash registers -- and tablets installed in restaurants to allow diners to see and order directly from menus.
Oracle said the acquisition would have a positive impact on its results immediately.
Micros was founded in 1977 in Columbia, Maryland, near the US capital Washington.