A new urea potentiometric biosensor based on all-solid-state (without inner liquid contacts) technology has been developed. Potentiometric transducers consisting of selective poly(vinyl chloride) (PVC) membranes directly applied onto electrically-conducting composite materials ([0-3] graphite/epoxy composites) has been previously developed in our laboratory. This all-solid-state construction procedure has been extended to the preparation of urea potentiometric biosensors using a new enzyme-immobilization technique based on the deposition of the biocatalyst layer onto the active transducer surface by spraying a diluted solution of glutaraldehyde. The combination of these new simple technologies provides a wide range of adaptability and multifunctional designs for the resulting sensing devices. Furthermore, by using a PVC-matrix membrane as the support of the enzymatic layer, the detachment of the enzyme (urease) is considerably reduced since a better adsorption on the enzyme layer is achieved. The results obtained with this new type of urea potentiometric biosensor show a low response time (10 s) and a wide linear range (10−5 to 10−3 M) with a sensitivity of 55 mV per urea decade. A great gain is achieved in terms of stability with a lifetime of about 40 days in periodical calibration use. Additionally, a flow-through urea biosensor using the same type of potentiometric transducer and immobilization procedure has been constructed for the use in flow-injection analysis systems.