Lignin (poly-phenylpropane units) was precipitated from waste black liquor produced by paper manufacture from rice straw. The use of this lignin as partial substitution of phenol in phenol formaldehyde resin is investigated. The effect of different variables [e.g., lignin concentration, ratio of formaldehyde to phenol lignin (phenol þ lignin), temperature, and polymerization time on the properties of the produced resin is studied]. The effect of the chemical modification of lignin by oxidation, reduction, and hydrolysis on the properties of the produced phenol lignin formaldehyde resin is also studied. Hydrolysis of lignin by hydrochloric acid increases the reactivity between lignin, formaldehyde, and phenol in producing resin with good properties more than untreated lignin. Also, the percent of replaced phenol with lignin in the resin can be increased by hydrolysis of lignin with hydrochloric acid. So, the reactivity of lignin toward resin formation has the following sequence: hydrolyzed lignin > oxidized lignin with dichromate > treated lignin with sodium hydrosulfite.