Auto-thermal reforming (ATR) of acetic acid (HAc) from renewable bio-oil is an alternative route for hydrogen production, and a series of Ni/Mn(II)Al(III)O-x +/-delta catalysts were prepared via co-precipitation method and tested in the ATR of HAc. Different parameters including reaction temperatures, O/C molar ratios, gas-hourly space velocity (GHSV), and stability were investigated. The optimal Ni0.39Mn1.61 AlO4.31 +/-delta catalyst exhibited excellent catalytic performance in a 50 h ATR test: HAc was converted to H-2-rich gas with conversion near 100% and hydrogen yield at 2.7 mol H-2/mol HAc. Characterization results demonstrate that with strong interaction among nickel, manganese, and aluminum, a thermally stable spinel structure of MnAl2O4 over the MnO support was formed and restrained the growth of Ni particle; meanwhile, oxygen vacancies were found and were beneficial for oxygen transfer in the gasification of carbon. As a result, deactivation by carbon deposition and sintering was restrained. Moreover, high GHSV up to 120,000 mL/(g(cat).h) and fast response to startup were recorded, showing potential for hydrogen feeding via the ATR process.