This work presents an H∞ observer design for road profile estimation in the automotive semi-active suspension system. The dynamics of the quarter-car augmented with a nonlinear dynamic model of the semi-active damper are written into the descriptor system with road profile as the system states. Then an H∞ observer is developed to estimate the road profile using the onboard accelerometers as the observer's input. The objective is to minimize the effect of sensor noises on the estimation error using H∞ framework. The estimation approach is simulated on the quarter-car model of a scaled testbench of Gipsa-lab. Simulation results show the effectiveness of the proposed method.