The first museum to exhibits Six Dynasties relics will be built in Nanjing, so the ruin of City Wall of that period needs on-site conservation. Curtain grouting was adopted to block groundwater. Because the wall has been immersed in water for a long time, the effloresce of wall's surfaces has accelerated. Organic silicone materials such as fluorine-silicone (S130), polysiloxane (pelicoat) and short-chain siloxane (methyl-trimethoxysilicane) were tested to see if they are suitable conservation materials. These silicone materials were first applied on the samples in the laboratory. Results are evaluated based on appearance changes, contact angle, water absorption, water permeability, durability in complete immersion tests, appearance and quality changes in partially immersed tests. The results show that specimens after pelicoat and methyl - trimethoxysilicane treatment are relatively good. Meanwhile, the hydrophilic nature of bricks and the water - resistance of organic conservation films have an effect on the test samples depending on the physical and chemical properties of the test samples. These two organic silicones may be useful as chemical conservation materials for treating the city wall. However, their applicability should be judged only after on - site experiments.