This study was evaluated by changing the mass loss ratio and the strength maintenance ratios of the fibers after treatment. The fibers were treated with sodium hydroxide and hydrochloric acid solutions for different amount of times. The environmental resistance was analyzed by changing the time of treatment in NaOH and HCl solutions. The fibers’ surface corrosion morphologies were analyzed using the optical microscope. The acid resistance was much better than the alkali resistance for the basalt and slag fibers. Nevertheless, the situation for the glass fibers was different: the acid resistance was almost the same as the alkali resistance. Between the two types of aqueous environments evaluated, the alkali solution is the most aggressive to the fibers’ surface.