Rammed earth in a built environment has vapor diffusion characteristics and humidity control ability each of which are respectively attributed to the porous structures and the hydrophilic properties. Indeed, these structures and properties, which allows easily absorbing water parti-cles, hence, affecting the durability of a rammed earth wall. This paper presents the water repel-lency method for rammed earth walls which synthesizes siloxane copolymers containing fluo-rine. The water-repellent properties are investigated by measuring the contact angle, water ab-sorption rate, and compressive strength after spray coating with the synthesized siloxane co-polymers on the surface of the rammed earth specimens under study. The water contact angle of the specimen coated with a siloxane copolymer containing 10 mol.% of a silane monomer with a fluorine group is about 140o. The water absorption of the specimen obtained after immersing in water for 24 hours is low at about 3.5 wt.%. In addition, the compressive strength is remained more than 80% of the corresponding strength of the specimen which is not immersed into water. It is confirmed that the use of a 10% by volume of the siloxane copolymer containing the fluo-rine group may assure the water-repellent performance and the economic competitiveness.