This paper presents a study on nanocomposites formation in ZnO-SiO2 systems with different ZnO:SiO2 molar ratios (1:4, 1:1, and 4:1), prepared employing a sol-gel method modified by an original procedure. The evolution of ZnO-SiO2 systems depending on the composition and temperature was studied by thermal analysis, Fourier transform infrared spectroscopy, X-ray diffractometry and transmission electron microscopy. Zn(II) carboxylate was synthesized in situ in hybrid silica gels by redox reaction between zinc nitrate and 1,3-propanediol. Its thermal decomposition at low temperatures led to ZnO dispersed in the pores of silica matrix. Only for the 4:1 system, at 400 and 600 degrees C, ZnO nanocrystallites (average size similar to 9 nm) embedded in the amorphous silica matrix were obtained, the other systems being amorphous. Whatever the mixture composition is, above 600 degrees C, ZnO reacts with SiO2 to form zinc silicate. At 800 degrees C, for both 1:4 and 1:1 systems, poor crystallized beta-Zn2SiO4 and alpha-Zn2SiO4 phases embedded in silica matrix were formed. Increasing the temperature, at 1000 degrees C, only for 1:1 system, beta-Zn2SiO4 phase turned into single phase alpha-Zn2SiO4 (average crystallites size 28.3 nm). For 4:1 composition, at 800 and 1000 degrees C, systems consisting of ZnO and alpha-Zn2SiO4 nanocrystallites dispersed in silica were obtained. (C) 2016 Elsevier B.V. All rights reserved.