You certainly can use them, they're just not optimized for acoustic guitars like acoustic strings, though. I put 9s on an acoustic once (I'm a tinkerer) and it did not go well. would not intonate, sounded tinny and bad. Like you'd expect from ultra thin strings on an acoustic. I imagine if you use 11s, 12s, or 13s, they'd work just fine, probably just a different, less full sound. Since acoustic strings cost roughly the same, I can't see a reason to do that, in most scenarios. Maybe if you have excess electric strings around. but in a pinch, they would certainly work.