Phenol-formaldehyde/silica hybrid aerogels with different degree of hydrophobicity were successfully synthesized via high temperature sol-gel polymerization. Tetraethoxysilane (TEOS) and methyltri-ethoxysilane (MTES) were used as precursor and co-precursor of the hydrophobic silica-based phase, respectively. The hydrolysis step of silica based sols were conducted by acid catalyzed reactions and HC1 was used as hydrolysis catalyst. The chemical structure of prepared hybrid aerogels was characterized by Fourier Transform Infrared spectroscopy (FT-IR). The effect of MTES/TEOS proportion and catalyst content on the morphology and microstructure of samples were investigated by FE-SEM and C, Si mapping analysis. The acid catalyzed hydrolysis of TEOS and MTES sols leads to formation of a sol with primarily silica particles in the organic-inorganic hybrid sol and varying colloid growth mechanisms were occurred with change in MTES and HCI molar ratio. With the increasing of MTES content, the microstructure of samples changed from uniform colloidal network, core-shell structure to polymeric structure with a huge phase separation. The increasing of HC1 mole fraction leads to smaller particle size. Moreover, the shrinkage of samples was decreased and water contact angles of the resulted aerogels were increased from 40 to 156.8 with the increases of MTES content. (C) 2017 Elsevier Inc. All rights reserved.