A modified disturbance observer is proposed for non-minimum and dead-time processes. The adverse effects of time delay on systems can be compensated effectively by utilizing a phase lead compensator, which makes it more effective for the system to reject external disturbances and internal disturbances caused by model mismatches. The step and ramp disturbances can be rejected efficiently through the design of a filter. Rigorous performance analysis and robustness stability analysis are presented. The proposed method is also suitable for high-order dead-time processes and minimum phase dead-time processes. The proposed structure is simple for application in practice. Simulation results show that the proposed method provides a superior performance of set-point tracking, disturbance rejection and robustness in case of model mismatches.