Ordinary fillers possesses an excellent initial rheological properties to epoxy adhesives, but under several months’ storage or under high temperature cure conditions, they can lose their sag resistance. The reason for failure mechanism of the thixotrope is concluded to be due to the preferential absorption of the epoxy groups of the sealant on the surface groups of hydrophilic fillers. Because of that, strength of the silica network in the epoxy system is extremely reduces. Where as, Our synthetic fillers gives excellent rheological properties and much improved aging properties to the epoxy adhesives and sealants.