This paper reports result of a study conducted to evaluate the aging properties of isobutyl triethoxysilane coating used in marine concrete. The silicone coating was brushed to the surface of mortar specimens and the aging properties of the silicone coating were investigated by thermal aging and ultraviolet (UV) aging. The water absorption of the mortar specimens applied with the silicone coating increases with the extension of the aging time. And the higher aging temperature, the bigger the water absorption. Because of the combined effect of light and heat, water absorption of specimens after UV aging at 60 °C is larger than that after thermal aging in the same temperature. In addition, noticeable variation in aging properties of the same silicone coating by different manufacturers is noted.