A series of all sol-gel organic-inorganic nonlinear optical materials based on the prepolymers of melamines and an alkoxysilane dye (ASD) were investigated. The NLO-active ASD containing nitroazobenzene was incorporated into the melamine matrices with different weight ratios. This all sor-gel type is shown to have the advantages of simultaneous polymerizations, and better compatibility between two components due to residual hydroxyl and silanol groups after curing. The simultaneous route is often used to avoid significant phase separation in a multi-component system. SEM results indicate that the inorganic networks are distributed uniformly throughout the organic networks on a molecular scale. The silica particle sizes are well under 1 mu m. This series of all sol-gel materials exhibits large second-order optical nonlinearity (d(33) = 10-54 pm/V at 1064 nm, and 3-17 pm/V at 1542 nm) after poling and curing. Temporal stability of the effective second harmonic coefficient at 100 degrees C is also reported.