First live action movie from a cartoon.

Was it The Flintstones? It was made in 1994.

Masters of the Universe is older by a fair bit - released in 1987.

Popeye, which starred Robin Williams, is from 1980. I wouldn’t be surprised if there’s something older than that though.

If you count superheroes, there were lots of Superman and Batman and Spider-man movies over the years, long before 1987. Here’s a 1943 Batman adaption:

OK, I realize now the OP asked for cartoons, not comics, so mine may not apply.

I’m not sure if this is a hi-jack or what. It isn’t quite a nit either. But in a roundabout way, He-Man kind of started as a live action, then a cartoon, then back to live action. Does anyone remember the 7-Up (I think) commercial a short while ago that had the ‘Slug’ product line with the movie idea thrown in at the end? I think it was sort of like that.

From IMDB’s triva page for Conan the Barbarian:

Was there ever an animated “Blondie” before the 80s? There were all those Blondie movies in the 30s with Arthur Lake and Penny Singleton.

I can think of lots of comic strip-to-live action movies, but I’m drawing a blank on anything earlier than Popeye.

I’m stumped too. I can think of dozens of live action movies based on comic strips or comic books, going back to the 1920s. But live action features based on animated cartoons, nothing before Popeye (1980).

How about LI’L ABNER, made in 1959? (Before you complain that LI’L ABNER is a comic strip, let me point out that in the forties Columbia made some [justifiably unremembered] animated cartoons based on the strip.)

Personally, I think that the 1959 LI’L ABNER is the best live-action movie based on a cartoon or comic strip. Rather than rely on a bunch of overdone makeup effects, the producers assembled a cast of actors who looked exactly like their cartoon counterparts!
Example: when we first meet Abner (Peter Palmer), he is bent over the motherly knee of Mammy Yokum (Billie Hayes), having his britches patched as Pappy (Joe E. Marks) watches. She finishes, Abner stands up, and he is nearly twice as tall as either of his parents–and it is NOT a trick shot!

Even more wonderful, Julie Newmar steals the entire movie without speaking a single word.

Superman: The Movie was released in 1978. And there were Superman cartoons by then, weren’t there? I know the comic books were first (and the movie is based on the comics more than anything else) and there was also the live-action T.V. series from the 50’s, so maybe this doesn’t count.

Max Fleischer did a series of excellent Superman theatrical shorts in the early 1940s.

Popeye, incidentally, had a very successful comic strip before becoming a cartoon star. (The early Popeye cartoons were done by Fleischer, too.)

There was an animated Superman in 1941, and a live action version in 1948.

There was also a live-action L’il Abner in 1940, but this doesn’t count, since the first cartoon version was in 1944.

However, both the animated and live films of L’il Abner and Superman were spinoffs of a comic (and L’il Abner was actually taken from a Broadway show). Popeye also had his origin in the comic pages, though his cartoons were much more popular and successful than either of the others. So we have to take all three, or forget them all.

If you eliminate movies based on comic books and comic strips (whioch, I think, is what the OP wanted), then the first movie based upon a clear Cartoon source was 1982’s Boris and Natasha, starring Dave Thomas and Sally Kellerman as the Jay Ward duo. No Rocky or Bullwinkle in this misguided effort:

Dan. I jusy looked again, and note that it said 1992. That can’t be right. I coulda sworn the film was older than that. Even if it’s 1992, though, it prtedates Flintstones.