A method for fabricating microfluidic structures is provided. The method includes: a belt is provided and an adhesion layer is formed on at least one surface of the belt; the belt is cut for forming a first microfluidic channel thereon, wherein the first microfluidic channel has an accommodating space; a second microfluidic channel is provided, wherein a line-width of the second microfluidic channel is smaller than a line-width of the first microfluidic channel; the second microfluidic channel is disposed in the accommodating space of the first microfluidic channel; and a substrate is adhered to the belt via the adhesion layer.