A predictive model for cytotoxicity of 20 and 50nm silica nanoparticles has been built using so-called optimal descriptors as mathematical functions of size, concentration and exposure time. These parameters have been encoded into 31 combinations ‘concentration-exposure-size’. The calculation has been carried out by means of the CORAL software (http://www.insilico.eu/coral/) using three random splits of the obtained systems into training and test sets. The statistical quality of the best model for cell viability (%) of cultured human embryonic kidney cells (HEK293) exposed to different concentrations of silica nanoparticles measured by MTT assay is satisfactory.