We have studied an experimental method to evaluate the penetration depth of total-reflection x-rays, which is an important factor for total-reflection x-ray analysis. The penetration depth can be evaluated by measuring the takeoff-angle dependence of x-ray fluorescence. We have developed a new glancing-incidence and glancing-takeoff x-ray analytical apparatus. Using this apparatus, we evaluated the penetration depth of Mo Kα into a GaAs wafer. The experimental results agreed well with the theoretical penetration depth.