Provided are an active matrix substrate having a reduced driving voltage and excellent adhesion between a dielectric layer and a water-repellent layer and a microfluidic device including the substrate. The active matrix substrate includes an array electrode, a dielectric layer covering the array electrode, and a first water-repellent layer in this order on a first substrate. The dielectric layer includes a silicon nitride film located on the side in contact with the first water-repellent layer, and the silicon nitride film has a surface layer region containing oxygen in the surface on the side in contact with the first water-repellent layer.