Calcium oxides with a specific surface area between 4.5 m(2) g(-1) and 62.5 m(2) g(-1) were obtained by calcination of scallop shells, following by methanol-assisted dry nano-grinding. Three distinct phases are formed on the surface of these catalysts during nano-grinding: calcium methoxide, calcium hydroxide, and calcium oxide. The effects of specific surface area and active surface phase composition on the catalytic activity of calcium oxide during methanolysis of soybean oil were investigated. The properties of the calcium oxide before, during, and after methanol assisted dry nano-grinding were studied by XRD, FTIR, and nitrogen gas adsorption based on the BET method. The ground calcium oxides were found to be effective in catalyzing the methanolysis of soybean oil, with the optimal catalyst producing a 72.3% ester yield after 20 mins of reaction. The improvements in rate of reaction were attributed to the rapid formation of calcium diglyceroxide during the initial stages of methanolysis. A combination high specific surface area and effective active phases on the surface of the calcium oxide catalysts is correlated with reductions in mass transfer limitations in the early steps of the reaction, indicated by the rapid formation of calcium diglyceroxide. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.