PURPOSES: Surface treatment is a favorable method in the pavement preventive maintenance. This study (Part Ⅰ) aimed to develop the low viscosity filling material for waterproof characteristics and high penetrable and weather resistance, and a series of companion study (Part Ⅱ) presents the coating characteristics and performance analysis using field and lab tests. METHODS : Hydrophobic characteristics of the advanced surface treatment material are observed and measured the filling depth and the permeability for sand and asphalt pavement specimen using the water absorption test and permeability test, X-RAY CT test. Color difference for the weather resistance using ultraviolet ray accelerated weathering test is compared with asphalt pavement specimens. RESULTS : The developed material shows the decreased water absorption and increased impermeable effect because of the hydrophobic characteristics. It is found that the filling depth is about 6mm and weather resistance is better than asphalt pavement specimen. CONCLUSIONS: The advanced hydrophobic - low viscosity filling treatment material is developed in this study (Part Ⅰ) to improve the waterproof characteristics and high filling capacity and weather resistance for the pavement preventive maintenance.