A method for fibrillation of cellulose includes the following steps: introducing fiber pulp of anionic cellulose at a consistency of 1 to 4% into a homogenizer, and homogenizing fiber pulp in the homogenizer at a pressure of 200 to 1000 bar, advantageously 300 to 650 bar, and by using 2 to 4 passes through for the same fiber pulp under these conditions, and after passes through, taking pulp from the homogenizer, which pulp has been fibrillated by homogenization to a degree than can be expressed as Brookfield viscosity exceeding 10,000 mPa·s (consistency 0.8%, 10 rpm).