Robust autopilot design for bank-to-turn (BTT) missiles under disturbances and uncertainties is investigated in this article using the disturbance observer concept. It is well known that the BTT missile dynamics undergo substantial change during its flight. In this disturbance observer-based control (DOBC) setting, the influences caused by parameter variations are merged into disturbance terms and regarded as parts of the lumped disturbances. Disturbance observers are employed to estimate the lumped disturbances, and then a disturbance observer-based robust control (DOBRC) method is proposed in this article to compensate the influences of parameter variations and the disturbances from the output channels. Similar to the baseline linear quadratic regulator design, the DOBRC is analysed and designed using linear techniques. Very promising performance has been achieved for the BTT missile as shown in simulation. It is demonstrated that DOBC approach provides a simple, intuitive, and practical solution for many challenging control problems where systems are subject to significant external disturbances, and uncertainties such as BTT missiles.