Biomass is considered as a source of liquid and different chemicals and has led to the development of various research programs. The extraction yield of supercritical fluid extraction (SFE)from the hazelnut shell samples increased with an increasing amount of potassium hydroxide (KOH) and temperature. For example, it increased from 17.8 to 26.9% for a 20% KOH run and from 42.6 to 49.3% for a 100% KOH run with increasing temperature from 517 to 563 K. The utilization of modified lignin from supercritical fluid extracts of the hazelnut shell, as a copolymer in lignin-formaldehyde (LF) resin binders, was studied. The modified lignin was tested in preparation of a LF resin adhesive.