Railway structures applied to high-speed railways must achieve high performance in terms of strength and deformation characteristics. This requirement has led to the widespread use of geosynthetic-reinforced soil (GRS) structures. For the design of GRS structures, it is important to evaluate not only the tensile strength of the geosynthetic but also the pullout stiffness (spring constant of geosynthetic). Hence, a series of cyclic pullout loading tests were conducted to evaluate the pullout characteristics of various types of reinforcement embedded in the soil. Moreover, these test results were compared with the results of the in-isolation tensile tests with the same loading histories. The experiments revealed that the pullout stiffness increased with an increase in the confining pressure and in-isolation tensile stiffness, but decreased with an increase in the relative displacement between the soil and reinforcement. Although the pullout stiffness was found to be affected by factors such as experimental conditions and type of reinforcement, a similar trend was observed in the results of several other tests, when examining the relationship between the normalized pullout stiffness and the average strain generated in the reinforcement. This interesting correlation can be taken into account during the design of GRS structures that support bridge girders.