Silicon (Si) has long been known to play a major physiological role in certain organisms, including some sponges and many diatoms and higher plants, leading to the recent identification of multiple proteins responsible for silicon transport in a range of algal and plant species. In mammals, despite several convincing studies suggesting that silicon is an important factor in bone development and connective tissue health, there is a critical lack of understanding in biochemical pathways that enable silicon homeostasis. Here we report the identification of a mammalian efflux silicon transporter, namely Slc34a2 (also known as NaPiIIb), which was upregulated in the kidneys of rats following chronic dietary silicon deprivation. When heterologously expressed in Xenopus laevis oocytes, the protein displayed marked silicon transport activity, specifically efflux, comparable to plant OsLsi2 transfected in the same fashion and independent of sodium and/or phosphate influx. This is the first evidence for a specific active transporter protein for silicon in mammals and suggests an important role for silicon in vertebrates.