<p>Railway vehicles running at high speeds experience hunting motion, which is a flutter-type self-excited oscillation. The occurrence of hunting motion is primarily prevented by installing yaw dampers, but this comes with the drawback of performance deterioration. To overcome this limitation, gyro dampers can be used to stabilize hunting motion. Linear analysis has shown that an increase in the gyro’s rotational speed leads to an increase in the linear critical speed, which is the running speed at which hunting motion occurs, as determined through the stability analysis of a trivial equilibrium point. However, the influence of the gyroscopic effect on nonlinear phenomena, such as the Hopf bifurcation of railway vehicles, has not been elucidated. Understanding the nonlinear characteristics of railway vehicles is necessary to predict the occurrence of hunting motion when running below the linear critical speed, and the hunting motion amplitude. This study elucidated the influence of gyro rotation on the Hopf bifurcation of railway vehicles. Nonlinear analysis was performed on a model of a single railway wheelset with a gyro, with consideration to representative cubic nonlinearity, and the amplitude equation for hunting motion was derived. The analysis of the amplitude equation confirmed that an increase in the gyro’s rotational speed transforms the nonlinear feature of Hopf bifurcation from subcritical to supercritical. Additionally, the results were verified experimentally using a single wheelset with a gyroscopic damper and a roller rig.</p>