Matric potential, a crucial factor for plant water relations, is the potential energy of water in soil and matric potential sensors are expected to plays an important role in precision farming. We propose a low-cost soil matric potential sensor composed of electrodes fabricated on thin PET film and gypsum plate covering the electrodes. We use microcontroller to measures capacitance that represents volumetric water content (VWC) of the gypsum plate. From this VWC value, we can easily calculate the matric potential of surrounding soil. Since the proposed sensor is composed only of inexpensive materials, we believe soil matric potential sensor can be implemented within affordable price for farmers.