The present invention relates to a novel pulp composition for paper or solid board production comprising an oxidized recovered paper pulp and/or an oxidized mechanical pulp into which from 1 to 500 mmol of carboxyl groups per kg and from 1 to 200 mmol of aldehyde groups per kg have been introduced by oxidation. The invention also relates to paper and solid board based on such a pulp composition and also to a process for producing such paper or solid board. The invention also relates to the use of oxidized recovered paper pulp and/or oxidized mechanical pulp for improving the retention and drainage properties of a pulp suitable for producing paper or solid board. The invention further relates to the use of oxidized recovered paper pulp and/or oxidized mechanical pulp for improving, i.e., increasing, the dry strength of paper and solid board.