The Sewage Sludge (SS) is generated from the treatment of urban effluents and, as it contains both plant nutrient, mainly N and P, and organic matter, has been applied in croplands. However, as sludge may also contain potential contaminant elements, the main concerns on the agricultural use of sludge are the adverse effects on the environment and on the human health. Thus it is important to investigate the availability of inorganic toxic elements to crops (phytoavailability). The main methods for assessing phytoavailability are based on the use of chemical extractants, such as acid or chelating agent solutions, but none of these methods adequately predicts Nickel (Ni) availability to plant, since extractants only act as chemical agents and do not simulate the physiological activity of roots and plant. The radioisotopic L-value is the better method for evaluating phytoavailability of toxic elements, since plants are grown in isotopically equilibrated soils and also are used to measure element concentration and radioactivity. The objective of this work was to evaluate the phytoavailability of Ni as affected by the pH in sludge amended-soil, using the ⁶³Ni L-value method. The soil used was an Oxisol collected from the upper 0-20 cm layer, Piracicaba, State of São Paulo, Brazil. The pH of soil was adjusted approximately to 4.0, 5.0 and 6.0 by incubation with a mixture of Ca and Mg carbonates. The soil was placed in pots, treated with domestic SS in doses equivalent to 0, 15, 30, 45 and 60 t/ha (dry basis), incubated for 30 days and labeled with 148 kBq (4 µCi) of ⁶³Ni solution. The sludge, named “Jundfertil”, was obtained from the Sanitation Company of Jundiaí, São Paulo, Brazil. The test crop was the maize (Zea mays L.), single hybrid P30F80, which was grown for 40 days, and above ground parts and soil samples were collected, prepared and analyzed for total Ni and 63Ni radioactivity. The obtained data showed an increase on: above ground dry matter weight, Ni accumulated on corn, Ni-DTPA extracted from soil, and total acidity (H + Al); while a decrease on: L-value and soil pH, due to the doses of sludge. It was also observed that the soil pH had a strong influence on the chemical and physiological availability of Ni. The concentration of Ni extracted by DTPA increased with the decrease of soil pH, while the L-value decreased. It was concluded that, in sludge amended-soil, the Ni availability increases chemically (DTPA) and decrease physiologically (L-value) with increasing soil acidity. Keywords: sewage sludge, nickel phytoavailability, isotopic L value, ⁶³Ni.