AbstractIn this work, wet strength paper was prepared from quantitative filter paper pretreated with NaOH-thiourea-urea aqueous solution. The effects of alkali concentration, soaking time, freezing time, and washing time were evaluated through single factor experiments. The optimum conditions were found to be an alkali concentration of 8%, soaking time of 2 seconds, freezing time of 15 minutes, and washing time of 10 minutes. Under these conditions, the wet tensile strength of the modified paper could be increased to 33% of the dry tensile strength and 400% of the wet tensile strength of the body paper. Also, the wet burst strength could be improved to 200% of the dry burst strength and 2400% of the wet burst strength of the body paper. However, there were no significant effects on the structure of the functional groups or crystalline region. Also, there was no toxic material released during the treatment, and the treatment solution was recyclable and environmentally friendly.