Spent catalyst from manufacture of sulfuric acid production (main elemental composition: 3.5% V, 0.63% Ni, 7.9% Fe and 9.64% Si) can be used as a secondary source of vanadium and nickel. Extraction of these metals was studied using two different leaching systems (alkaline and acidic). Statistical design of the experiments and ANOVA (analysis of variance) were performed in order to determine the main effects and interactions of the factors under research, which were roasting, leaching temperature, concentration of the leaching reagent (H(2)SO(4) and NaOH), liquid/solid (L/S) ratio (at 100 mL of liquid reagent), and presence of hydrogen peroxide. The results obtained after acidic treatment show that nickel extraction yield of 96% is achieved after roasting at 600 degrees C, followed by leaching with 5mL/g 1 M sulfuric acid at 80 degrees C for a 30 min reaction time. The highest vanadium extraction yield was 59% after roasting at 400 degrees C and leaching at 80 degrees C by 0.3 M sulfuric acid for 6 h and 10 mL/g L/S ratio.