Filler loading effects in both the thermal stability (TS) and thermal conductivity (TC) of ED-20 epoxy filled with bare (MLG) or oxidized multi-layered graphene nanoplatelets (MLGO) have been experimentally and theoretically studied. The particles were of about 5x5m in lateral size, about 50nm in thickness, and of the specific surface area similar to 790m(2)/g. The filler's mass loading varied from 0.5 to 5.0%. TS studies have been performed by the temperature-programmed desorption technique with mass spectrometric detection of volatile moieties. The TC has been measured using the ASTM C1114 standard test method and modeled by equilibrium molecular dynamics simulations via LAMMPS package. TS has proved to be enhanced in MLG nanocomposites and deteriorated when using MLGO fillers, compared to those of the neat epoxy. For both the MLG and MLGO nanocomposites, volatile-moiety outputs showed non-monotonous loading dependences, whereas TC exhibited monotonic increase with increasing loading. It is shown that the TS and TC can be improved simultaneously in these nanocomposites. The likely involvement of the interfacial interaction mechanisms behind these effects is addressed.