"Beastmaster" star Marc Singer had a scary trip to the hospital this weekend ... TMZ has learned the actor was taken by ambulance after experiencing some pain.

Sources tell TMZ ... paramedics responded to Marc's Los Angeles-area home Saturday shortly after 2 PM and transported him to a nearby hospital.

We're told doctors ran tests and kept him overnight ... but thankfully, everything came back fine, and he's expected to be released Sunday.

It's unclear what caused the pain for the 78-year-old.

Marc is best known for starring in the 1982 fantasy film "The Beastmaster" and its sequel, "Beastmaster 2," along with the sci-fi miniseries "V."

He's also appeared on the long-running soap opera "The Young and the Restless."