Dissolution rates in acidic solution of nickel oxide prepared in air from carbonate and hydroxide salts at 550, 700, 1100 and 1450 °C are compared. The powders were pre-characterised by thermal analysis, B.E.T. surface area measurement, transmission electron microscopy, X-ray and electron diffraction and infrared spectroscopy. The carbonate decomposition process is considerably more energetic than that of the hydroxide. The rates per unit surface area for the ex-carbonate oxide are more than five times higher than those for the ex-hydroxide oxide at 550, 700 and 1100 °C annealing temperatures, but comparable at 1450 °C. The 700 °C ex-carbonate oxide shows anomalously high, initial rates, at <10 monolayer-equivalents removed, attributed to surface reduction. All samples show increases in rate with extent of dissolution owing primarily to surface roughening and increased kink site densities. The results are discussed in relation to excess (over equilibrium) surface and bulk defect concentrations introduced by decomposition proces, and modified by subsequent annealing.