In this work, Taguchi method was employed to elaborate the effects of temperature, concentration and immersion time of typical acids (HCl, H2SO4, HNO3) on the morphology and tensile strength of basalt fiber (BF). The results showed that the corrosion behavior of BF was controlled by the ion-exchange process with presence of H+ ions, and irregular and spiral cracks were formed during this process, which led to the severe degradation on the tensile strength of fiber. Besides the governing role of H+ concentration in acids, SO42- also aggravated the corrosion in sulfuric acid with precipitant of CaSO4. The reasons behind the acid-induced low-energy crack opening paths were given to illustrate the formation of spiral cracks on fiber surface in acids. The ubiquitous axial defects were revealed on fiber surface, and comparative results confirmed that such defects originated from the scratching between the filament and bushing during the fiber spinning process.