Though he dabbled with some odd looking Washburn guitars in the 80s, Ace is strongly associated with Les Pauls — and he always played Les Pauls with KISS. He started with a sunburst Standard and later switched to his more famous three pickup Custom. The classic Frehley tone comes from the three pickup Les Paul Custom with DiMarzio Super Distortion humbuckers. Ace rarely uses anything other than the treble pickup — in fact — the neck pickup is a fake and hides a smoke bomb that he uses during his solo spot. Gibson issued an Ace Frehley model Les Paul in the 90s.

Ace runs the guitar straight into a 100 watt Marshall head. "There's nothing like a Les Paul through a Marshall for that hard rock sound. I've tried every setting and for me, you take a 100 watt head and put every knob on 5. Sounds pretty cool." Ace is not into effects. He's used an old Vox wah on a couple of tracks, and aside from some delay added at mixdown on a few tracks, that's it.

Ace and Paul Stanley normally play distinctly different parts and have totally different sounds. Ace's tone is thicker and more overdriven; Paul is more midrangey and biting. Paul frequently used a Gibson Firebird or an Ibanez Destroyer with DiMarzio Super II pickups to compliment Ace's sound. In the studio, Ace likes to use vintage Pauls, Strats, and Teles. He'll often double his primary rhythm part with a Strat or Tele through a Fender Harvard combo, or an acoustic guitar.
(quoted from ace's fansite)