The manuscript describes the key aspects of Zn-Al mixed oxides prepared by different methods (the so-called urea method and co-precipitation methods using either NaOH/Na2CO3 alkaline solution or solution of NaOH) affording high conversion and selectivity values in aldol condensation of furfural with acetone. The structure, composition and acid-base properties of Zn-Al mixed oxides were described by using of TGA, XRD, N-2-adsorption, TPD-NH3/CO2 and in-situ diffuse reflectance spectroscopy and correlated with the catalytic performance of a series of Zn-Al mixed-oxides catalysts. Along with the impact of specific surface area and basicity on the furfural conversion, the conversion of furfural also increased with the increasing value of the edge of UV-vis spectrum of Zn-Al mixed oxide reflecting ZnO-Al2O3 interaction. We have introduced a simple method based on diffuse reflectance spectroscopy with a potential to predict furfural conversion over Zn-Al mixed oxides in aldol condensation of furfural with acetone.