A series of the organically modified inorganic NLO sol-gel materials based on the prepolymer of alkoxysilanes and an alkoxysilane dye (ASD) have been investigated. Optically clear samples exhibit large second-order optical nonlinearity (d(33) = similar to 10.8-54.0 pm/V at 1064 nm) after poling and curing at 220 degreesC for 1 h. The thermal behavior of these NLO sol-gel materials was studied by temperature-dependent dielectric relaxation. The results indicate that the crosslinking density of cured NLO sol-gel materials was increased with increasing alkoxysilane content. Subsequently, better temporal stabilities were obtained for the poled/cured NLO sol-gel materials with a higher alkoxysilane content. Moreover, the structural influence of alkoxysilanes on the thermal behavior and second-order nonlinearity was also studied for these NLO sol-gel materials.