Cotton linter pulp and paper pulp were subjected to hot refining with potassium and sodium hydroxide in the presence of sodium sulfide at concentrations of 5% and 20%. The resulting changes in their chemical, physical, and submicroscopic properties as well as their mercerization depth were studied. The addition of sodium sulfide during hot sodium or potassium hydroxide refining of the pulps resulted in a small increase in α-cellulose content of the cotton linters. Remarkable increase was observed in the case of the paper pulp as well as in the resulting decrystallization, and it increased the heterogeneity of the macromolecular structure of both pulps. This led to an increase in the swelling ability of the fibers as revealed from the results of water retention value (WRV), liquor retention value (LRV), and sodium hydroxide retention value (NaOH RV). The addition of sodium sulfide to sodium or potassium hydroxide during hot refining of the cotton linters or to sodium hydroxide during refining of the paper pulp led to the reduction in the degree of polymerization and to improvement in the reactivity towards xanthation. This was in contrast to the results of the alkali refining of the paper pulp with a mixture of potassium hydroxide-sodium sulfide in which the degree of polymerization was increased and the reactivity towards xanthation was decreased. The mercerization depth of the hot refined pulps was also investigated using FUR 1650 spectrophotometer absorption method. The cotton linters refined with a mixture of 5% sodium hydroxide-sodium sulfide possessed a higher degree of chemical purity and a good open and accessible fine structure and at the same time were characterized with a higher degree of polymerization suitable for use as a starting refined pulp for the manufacture of paper documents.