Abstract: A single stage method delignification process for pulps, preferably sulphite pulps. The improvement to conventional oxygen delignification process comprises in situ addition of a reducing agent substantially non-reactive with oxygen. The end result is a pulp having enhanced strength properties and higher viscosity. Sodium borohydride is the preferred reducing agent, and MgO is the preferred alkali source. Similar results can be obtained with a two-stage oxygen delignification wherein the pulp is treated with the reducing agent in the first stage, and then washed and pressed conventionnally before proceeding with the oxygen delignification in a second stage.