This paper presents a thermo-mechanical model of spindles with rolling bearings. The heat generated in the bearings and the motor is transferred to the ambient air, the motor coolant and the spindle head structure. It warms the spindle up and causes thermal deformations of spindle parts. Thermal deformation affects significantly properties (internal loads, stiffness) of rolling bearings and need to be considered in predictive models of spindles’ dynamics. The structure of the transient model contains thermo-mechanical loops which update the model with respect to the instantaneous condition of the spindle. The changes of the bearings’ internal condition and stiffness are calculated using the Jones’ nonlinear theory. The thermo-mechanical spindle model predicts temperature distribution, thermal growth of spindle parts, and transient changes in bearing stiffness and contact loads under specified operating conditions. The predicted bearing properties are then used to estimate the variation of natural frequencies and dynamic stiffness of the spindle.