A new class of all organic sol-gel second-order nonlinear optical (NLO) materials based on hexa(methoxymethyl)melamine (HMM) was developed. Two NLO active chromophores, 4-(4’-nitrophenylazo)aniline (DO3) and 4-amino-4’-nitrobiphenyl (ANB), were incorporated into the melamine matrices. The samples exhibited second-order optical nonlinearity after poling and curing at 220-degrees-C for 30 min. DO3/HMM and ANB/HMM samples showed a second harmonic coefficient, d33 of 10.7 and 1.8 pm/V at 1064 nm, respectively. The temporal stability of both systems was studied at room temperature as well as at 100-degrees-C. Waveguide optical losses of samples at 633 and 830 nm were found.