Google said the Federal Circuit's ruling in favour of Oracle was a "devastating one-two punch at the software industry" that would chill innovation.
Oracle did not immediately respond to a request for comment.
The litigation involves how much copyright protection should extend to Oracle's Java programming language, which Google used to design the Android operating system that runs most of the world's smartphones.
Oracle is seeking royalties for Google's unauthorized use of portions of the Java language known as application programming interfaces (APIs), which are tools that allow different computer programs to talk to each other.
Google has said copyright protection should not extend to APIs because they are essential tools for creating software.
Google has also argued that its copying of them is permissible under the fair-use defence, which allows unlicensed use of copyrighted works for purposes such as research.
The closely watched litigation has already produced several reversals of fortune.
The Federal Circuit disagreed in 2014, leading to a second jury trial in 2016 on whether Google was shielded by the fair use defence.
Oracle argued during the 2016 trial that Google copied Java because it was desperate to enter the smartphone market and that internal emails showed company representatives believed they needed to pay for a license.
Google countered that the APIs were written for personal computers and it transformed them for use in smartphones in a manner that caused no economic harm to Oracle.
The jury sided with Google, denying Oracle's bid for about $9 billion in damages.
The Federal Circuit said in its 2018 decision that Google could not invoke the fair use defence because it copied the Java APIs verbatim and "for an identical function and purpose."
(Reporting by Jan Wolfe; editing by Grant McCool and Cynthia Osterman)