The Boston Herald, the state's conservative tabloid, endorsed Arizona Sen. McCain for president in an editorial posted online Thursday.
"There are times in this nation's history so perilous that they cry out for a steady, experienced leader, a person so trusted that we would put the fate of this country in his hands. This is one of those times, and Sen. John McCain is that person," the newspaper said.
It did not mention Romney, who led Massachusetts from 2003 to January of this year.
The newspaper also did not endorse anyone in the Democratic presidential race, breaking its tradition of choosing candidates in both parties.
Both the Herald and The Boston Globe, which announced its backing of McCain earlier this week, circulate in vote-rich southern New Hampshire, which holds the nation's first presidential primary on Jan. 8. Romney maintains a sizable lead there, but McCain is hoping to repeat his primary victory in 2000.
McCain also has been endorsed by the Union Leader, New Hampshire's largest newspaper.
Romney has brushed off the endorsements, citing his own, including from Republican Sen. Judd Gregg, the senior Republican in New Hampshire.
The Boston newspaper endorsements could provide fodder for former Arkansas Gov., who has pulled into first place and ahead of Romney in Iowa, which holds caucuses Jan. 3. Since losing the lead, Romney's campaign aides have taken to e-mailing daily missives about Huckabee written by people familiar with his record. They are headlined, "Those who know him best."