The present invention provides a process for preparing a paper or paper board of improved strength which comprises the steps of i) providing a cellulosic thick stock, ii) diluting the thick stock of step i) to form a thin stock, iii) draining the thin stock of step ii) on a wire to form a web, and iv) drying the web of step iii) to form paper or paper board, wherein the cellulosic thick stock of step (i) comprises organic polymeric microparticles, as well as paper obtainable by above process.