Mechanism and kinetics of cure reaction of Epoxy-silica nanocomposites from direct blending of DGEBA with nanoscale silica (NS) and with 4,4'-diaminodiphenylamine (DDA) or 4,4'- diaminobiphenyl benzidine (DAPB) as curing agents were investigated by FTIR and DSC. NS particles catalyzed the cure reaction, increased the rate constant (k), decreased activation energy (Ea), and shifted the exothermic peak temperature (Tp). Thermal stability of the cured samples was studied with TGA. The water diffusion behavior of cured samples was investigated and the diffusion coefficients (D) were calculated by using Fick’s law.