The bat Babe Ruth used to smack his 500th home run is expected to fetch upward of $1 million when it goes up on the auction block — 75 years after the historic blast.

The Louisville Slugger still has marks where the Babe’s bat hit the ball, and where he knocked mud off his cleats before slugging the historic blast in Cleveland’s League Park in 1929.

The Yankees legend gave the bat to buddy Jim Rice, the former mayor of Suffern in Rockland County, in the mid-1940s — and it sat in the corner behind the family TV for years, Rice’s son said.

Terry Rice, an attorney in Suffern, was born two years after Ruth died in 1948 — but grew up knowing the bat was a cherished heirloom.

“It was always there,” he told the Associated Press. “It was part of life. No one said I could touch it. I never took it out and played baseball with it.”

“For an inanimate object, it’s beautiful,” he added. “It’s in perfect condition.”

His father died in 1983 and passed on the bat to his wife. When she died in 1997 it fell to Terry Rice as a family heirloom — and he stashed it in a closet.

But it made him a nervous wreck.

“You couldn’t leave it out,” Terry Rice said. “I wasn’t enjoying it. It got to the point where we were worried about it.”

So, he talked his two older sisters to sign off on the sale and made a deal to peddle the bat at auction — where it’s expected to hit it out of the park.

“Babe Ruth is the king of the sports collectibles marketplace,” said David Kohler, president of SCP Auctions in California. “When a fresh Ruth item of such quality and historical significance as this one surfaces, it generates tremendous excitement throughout our industry.”

SCP sold the bat Ruth used on the inaugural opening day at the original Yankee Stadium in 1923 for $1.26 million in 2004.

The Sultan of Swat’s 500th shot sailed over the right-field wall at the Cleveland ballpark and rolled down Lexington Avenue. A fan picked the ball up and returned it to Ruth for an autograph and $20.

The Rice siblings, who will split the proceeds for the bat, have other mementos from the Babe, including an autographed ball and a signed photo.

Terry Rice said his dad would be “absolutely flabbergasted” if he knew he was selling the priced piece of lumber.

Bidding begins on Nov. 27 and closed on Dec. 14 at scpauctions.com.

With Post wires