Well, it was listed as all aluminum, but the seller typically deals in pawn shop type stuff, power tools, electronics, etc... the drop outs look way to minimal and clean to be aluminum welds, but I must confess, I dont know much about frame building. could very well be steel, one of the reasons I'm trying to get a hold of the builder, a peter dreesens in Pa. He rides for South Mountain Cycles in Emmaus, PA. I just found a ph# for the shop, no website, I'll give em a call on monday and hope the # is current. I'm gonna give her a spin mid day monday when the trails are empty. pray for my tires, as I"m sure they are the originals, though they still hold air at 100 lbs.