Although numerous studies have been reported in literature about extraction of lignin, in the current work lignin was extracted from pine straw, wheat straw, alfalfa, and flax fiber via organosolv treatment. The resulting organosolv lignin’s thermal properties and functional groups were studied.and placed in a conical flask. A mixture of 85% organic acid (ratio of formic acid/acetic acid mixture was 70:30 by volume) was added to the biomass in the flask at a fiber to liquor ratio of 1:8 and allowed to boil on a hot plate for 2h. After 2h, flask and its content was allowed to cool to ambient temperature. Fibers were filtered in a Buchner funnel and washed with 80% formic acid followed by hot distilled water.