The thermomechanical properties, thermal stability and flame retardancy of the organoclay-vinyl ester nanocomposites and the glass fiber reinforced plastic composites made from the vinyl ester nanocomposites matrix were studied. The results show that nanoclay addition increases both the storage modulus and glass transition temperature of the vinyl ester and glass fiber reinforced plastic composites due to the reinforcing effects and the molecular relaxing constraining effects of clay platelets. Both the vinyl ester and glass fiber reinforced plastic composites show different thermal degradation behaviors in nitrogen and in air due to the oxidizing effect of oxygen. Nanoclay has little effect on the thermal stability of vinyl ester in nitrogen, while increases the 2^nd peak decomposition temperature of vinyl ester in air, resulting from the shielding effect of silicate platelets. However, the thermal stability of the glass fiber reinforced plastic composites in both atmospheres is reduced by nanoclay with unknown reasons. The flame retardancy of vinyl ester and glass fiber reinforced plastic composites is significantly improved due to clay that promotes the formation of carbonaceous char platelets acting as mass and heat barrier. Glass fiber reinforcement alters the thermal dynamic, thermal degradation and combustion behaviors of the vinyl ester nanocomposites.