Method of producing a fibrous web

A method of manufacturing a fibrous web comprising a filler. According to the method, the filler is fed into the fibre slush and a fibrous web is formed of the filler-bearing fibre slush, and this web is dried at the paper or cardboard machine. The filler used is a composite material which comprises cellulose or lignocellulose fibrils, onto which light- scattering material particles have been precipitated. According to the present invention, the filler is brought into contact with the dispersant before it is mixed into the fibre slush. With this solution it is possible to significantly improve the light-scattering properties of papers and cardboards, without decreasing the retention of the filler.