<p>An accurate computation of the fundamental period of soil deposits, which is a significant part of dynamic characteristics, leads to the earthquake resistant design of structures and, therefore, seismic hazard mitigation. For this purpose, in this paper, an attempt has been made to present a rigorous solution for the fundamental period of three-layered linear elastic soil underlain by a bedrock subjected to SH wave propagation by utilizing the amplification function definition. The prediction accuracy of the presented solution is verified by comparing it with the numerical solution obtained with SHAKE program and the values obtained from earthquake data recorded in the specific number of instrumented geotechnical downhole arrays previously identified in the literature. The results are in close agreement with these values, which stems from the capability of the solution to take not only the values of thickness and shear wave velocity of layers but also the position of them. Apart from that, six approximate methods are employed for the sake of evaluation and comparison. Moreover, significantly, for different arrangements of three-layer soil deposits, normalized practical graphs that display the effect of salient model parameters on the fundamental period and simplify the solving process are provided.</p>