A novel chemiluminescence (CL) flow-through sensor for hydrogen peroxide is described. It is prepared by immobilizing hemoglobin (Hb) with the sol-gel method on the flow cell, and by electrostatically immobilizing luminol on strongly basic anion-exchange resin. Hydrogen peroxide is sensed by the CL reaction with Hb sensitive membrane and luminol bleeding from the ion-exchange column with immobilized luminol by hydrolysis. The calibration graph is linear in the range of 6×10−5 to 4×10−7 mol l−1 with a detection limit of 1.3×10−7 mol l−1 (3σ). A complete analysis could be performed in 1 min with a relative standard deviation of 1.7% for 5×10−6mol l−1 H2O2 (n=9). The sensor has been applied successfully to the determination of hydrogen peroxide in rainwater.