Si3N4-filled epoxy resin composite was fabricated employing liquid press molding method. Properties, such as thermal conductivity, dielectric constant of Si3N4-filled epoxy resin composite were evaluated, the effect of the content of Si3N4 and surface treatment of the filler was also considered. A silane coupling agent, namely NH2−(CH2)3Si−(OC2H5)3, was applied to functionalize the surface of Si3N4 filler. Experimental results showed that the thermal conductivity of the composites is strongly dependent on the filler and is dominated by the interface of epoxy resin and Si3N4 particles. As the Si3N4 volume fraction increasing, thermal conductance of Si3N4-filled composite was improved obviously, especially for that of silane-treated Si3N4 powder filled composite. Dielectric constant of the composite increases linearly, however, it still remains at a relatively low level (<5, at 1MHz).