Three types of modified silica nanoparticles were added sep. (40% by mass) as fillers to dimethacrylate resin-matrix, then light-cured and tested for usefulness of the composites in dentistry. The tests were made also for composites without any addn. of fillers. The addn. of fillers resulted in increasing the bending strength, flexural modulus and micro hardness as well as in reduction of diam. tensile strength.