"The F-35 program and cost is out of control. Billions of dollars can and will be saved on military (and other) purchases after January 20th," Trump said on Twitter.
The aerospace giant's shares dropped 2.6 percent in premarket trade after Trump's tweet.
A week before Trump won the Nov. 8 presidential election, the U.S. Defense Department and Lockheed Martin (LMT.N) concluded negotiations on their ninth contract for F-35 fighter jets after 14 months of negotiations on the deal of more than $6.1 billion, the Pentagon said.
Trump campaigned on a promise to cut waste in federal government.
Last week, he also used Twitter to target Boeing Co (BA.N) for its "out of control" costs on a new fleet of Air Force One planes, urging the federal government to "Cancel order!"