The reinforced concrete structures have been considered durable for a long time. But recently, it has been reported that they are deteriorated by alkali-silica reaction and/or reinforcement corrosion and so on. In the deterioration mechanism, water existing in concrete can be one of the main factors. Silane, which is one of hydrophobic impregnants, is applied on concrete to control water in concrete. In this paper, the effect of silane was evaluated by mass change, strain, and halfcell potential. Silane performed better for controlling the expansion of concrete by alkali-silica reaction and the reinforcement corrosion by chloride ion. However, when an excessive amount of reactive potential and/or chloride was included in concrete, it was difficult to restrain the deterioration in a long term. Silane was most effective when an water content in concrete was 85% and the concentration of silane solution was 40%.