Inorganic-organic hybrid crack-free xerogels were obtained using di-n-butyltin dilaurate(DBTL)as a catalyst containing tetraethoxyorthosilicate(TEOS)and hydroxyl-terminated polydimethylsiloxane(PDMS-OH)as a additive.We studied the effect of gelling time and sol pH on DBTL concentration.The xerogels structure was studied by FTIR,SEM techniquess.The results showed that the catalyst(DBTL)would substantially shorten the gelling time of the sol.With the addition of PDMS-OH,the viscosity of the sol increased while the gel time decreased.In addition,we noticed an improvement in the cracking of the xerogel with the addition of PDMS-OH.However,the xerogels were not opaque when mole ratio of PDMS/TEOS is higher than 0.153.Addition of silica nanoparticles at 1% w/v in sol could increased xerogels surface roughness and hydrophobicity and did not change color of the xerogels.The protective performance evaluated by its ability to resist acid rain revealed that the protective effects were satisfying.