With a View to improving the efficiency of particle trapping, the surface of glass air filters was chemically modified with (heptadecafluorodecyl) trichlorosilane (HFTS) in a vapor phase. The efficiency was greatly increased by the treatment with concurrent suppression of the rise in the resistance to air flow within a low level, while the treatment with (hexyl)trichlorosilane (HTS) was ineffective. Molecular orbital calculations on the clusters modeling the surface adsorbates indicated that the large dipole moment along the molecular chain axis of HFTS is responsible for the improvement of the particle trapping efficiency. It was further suggested that a well-ordered monolayer with the molecular orientation perpendicular to the surface plane serve for this purpose.