The boundary stabilization problem of a star-shaped type II thermoelastic system is considered, where there is a nonuniform bounded disturbance at the control end. A time-varying extended state observer is proposed to estimate and cancel the disturbance, thereby largely removing the uncertainties and simplifying the feedback control law design. The exponential stability is shown for the extended state observer, so are the well-posedness properties of the closed-loop system, all based on the linear operator semigroup theory. Finally, it is shown that the disturbances can be attenuated and the resulting closed-loop system can exponentially approach zero. Numerical simulations illustrate the effectiveness of the proposed control strategy.