A fully inkjet-printed disposable and low cost paper-based device for potentiometric Na+- or K+-ion sensing has been developed. A printed ionophore-based all-solid-state ion selective electrode on a graphene/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (G/PEDOT:PSS) nanocomposite solid contact and a printed all-solid state reference electrode consisting of a pseudosilver/silver chloride electrode coated by a lipophilic salt-incorporating poly(vinyl chloride) membrane overprinted with potassium chloride have been combined on a microfluidically patterned paper substrate. Devices are built on standard filter paper using off-the-shelf materials. Ion sensing has been achieved within 180 s by simple addition of 20 μL of sample solution without electrode preconditioning. The limits of detection were 32 and 101 μM for Na+ and K+, respectively. The individual single-use sensing devices showed near Nernstian response of 62.5 ± 2.1 mV/decade (Na+) and 62.9 ± 1.1 mV/decade (K+) with excellent standard potential (E0) reproducibilities of 455.7 ± 5.1 mV (Na+) and 433.9 ± 2.8 mV (K+). The current work demonstrates the promising possibility of obtaining low-cost and disposable paper-based potentiometric sensing devices potentially manufacturable at large scales with industrial inkjet printing technology.