A bismethacrylatesilane monomer (BMS) was prepared via selective Michael addition of aminopropyltrimethoxysilane (APTMS) to the acrylate groups of 2-methacryloyloxyethyl acrylate (ethyleneglycol acrylatemethacrylate, EGAMA). Sol-gel condensation of BMS in triethyleneglycoldimethacrylate (TGDMA) afforded in situ stable methacrylate-functional nanoparticle dispersions, with average nanoparticle diameter of 3-4 nm, as determined by means of element-specific transmission electron microscopy (TEM). Condensation in the absence of TGDMA could be achieved without gelation. Viscosities of the resulting nanoparticle dispersions were low, ranging from 12 to 1969 mPa s, shear-rate-independent and increased with the nanoparticle fraction, exhibiting hard-sphere behavior. The nanoparticle dispersions in TGDMA were employed as matrix for the preparation of photocurable acrylic nanocomposites. Mechanical properties such as compressive and flexural strength as well as Young's moduli (6000 to 8700 MPa) have been determined. Low volume shrinkage was observed upon polymerization. The volume shrinkage depended on the nanofiller fraction.