A novel sensing nano-film immobilized plant-esterase-monosulfonate tetra-Ph porphyrin (TPPS1) was prepared for the detection of di-Me Me phosphonate (DMMP), a stimulant of nerve agents. Several factors that influence preparation of the film, such as sodium alginate concentration, activation time, and adsorption time, were investigated. The morphol. and sensing property to DMMP of the film prepared under optimized conditions were characterized and analyzed by at. force microscope (AFM) and UV-Vis spectroscopy, resp. The results showed that the activity of immobilized plant-esterase was higher when sodium alginate concentration was 0.43 mol/L, activation time was 80 min, and adsorption time was 170 min. The nano-structure of the film had a good effect on its sensitivity to DMMP and lowered the detection limit. The interaction of TPPS1 with immobilized plant-esterase yielded a characteristic peak at 422 nm. Exposure of the immobilized plant-esterase-TPPS1 surface to DMMP resulted in a decrease in absorbance intensity at 422 nm due to the displacement of the porphyrin from the active site by DMMP. The loss in absorbance intensity at 422 nm was linearly dependent on DMMP concentration below 9×10-7 mol/L. DMMP concentration as low as 4.5×10-10 mol/L could be detected by the sensing nano-film.