Background Pyroaurite-based Mg Symbol of the Klingon Empire Fe oxides with varying Mg:Fe ratio were studied. The structural and acido-basic properties were examined by number of experimental techniques. The oxide properties were correlated with the catalytic activity in aldol condensation of furfural with acetone. Results Well-developed mesoporous structure was detected for all oxides. Peculiar continuous increase of concentration of basic sites and population of unsaturated strong basic O2- sites was observed with the rising amount of magnesium in the Mg Symbol of the Klingon Empire Fe oxide matrix. A relatively higher concentration of Lewis acid Men+ sites was shown for low Mg:Fe ratios. Unambiguous correlation between conversion of furfural and the density of strong basic sites was proved by combined catalytic and statistical analysis. The contribution of other basic sites was found significantly less important. The impact of both acid and basic sites on the composition of reaction products was discussed. Conclusions Mg Symbol of the Klingon Empire Fe oxides revealed good catalytic performance in the aldol condensation of furfural with acetone where samples with a high Mg:Fe ratio were significantly more basic and had relatively enhanced furfural conversion (nominal Mg:Fe ratio 10; furfural conversion 88% and selectivity to F2Ac 34%; reaction conditions: batch reactor; 50 degrees C; acetone/furfural = 10 mol L-1). (c) 2018 Society of Chemical Industry