The technique of diffusive gradients in thin films (DGT) for the measurement of Ni2+ in waters was developed using sodium poly(aspartic acid) (PASP) solution as the liquid binding phase in the liquid-type DGT devices (PASP DGT). The Ni2+ uptake of PASP DGT increased linearly with time (r(2) = 0.9990) with a DGT-labile fraction (Psi) of 98.04 +/- 1.76% in synthetic solution. The Psi values of Ni2+ were measured in spiked river water (37.82 +/- 2.79%) and spiked domestic wastewater (28.46 +/- 1.87%). The stability constant (log K) of PASP-Ni was 8.56, indicating that PASP can coordinate strongly to Ni2+. The binding capacity of PASP DGT decreased with increase of ionic strength, whereas it remained fairly constant in the pH range 4-9. The results show that PASP can be used as a binding phase in the liquid-type DGT device for the measurement of Ni2+ in waters.