Alonsotegi is a municipality in the province of Biscay, in the Basque Country region of northern Spain. It lies in the valley of the Cadagua River, along the BI-636 highway, approximately 8 kilometres from the centre of Bilbao.
Until the end of the 19th century, Alonsotegi was attached to the municipality of Baracaldo. It separated at that time and was officially recognised as an independent municipality in its own right.