The paper presents numerical results of prestress loss in the prestressed hollow core slabs by using few natural frequencies. Loss of prestress has been investigated by the 3D finite element method, by using ANSYS software. Loss of prestress is modelled by decreasing of prestressing forces in the 7 wire strand that simulated damage or severing of prestress strands. The prestressing force in the strands is applied as an initial stress. The effectiveness of using frequency percentage changes as an indicator of the loss of prestress and effectiveness of the proposed method are investigated using the planning of experiments and response surface technique. After selection of equation of regression, the parametric studies are carried out in order to determine the influence of the slab length, concrete strength and initial stress on the frequency percentage changes and study the dependence of the percentage changes on these parameters. The present study shows that natural frequencies percentage change is dependent on the span of slab and compressive strength of concrete.