Polyurethanes have been prepared from a prototype organosolv lignin by solution casting with polyethylene glycol (PEG) and polymeric methyl-diisocyanate (MDI). The effects of lignin composition and NCO/OH ratio on the mechanical properties and swelling behaviour of the derived poly urethane films were investigated. At low lignin content, flexible but weak polyurethanes were produced regardless of the NCO/OH ratio. Rather tough polyurethanes were prepared at intermediate NCO/OH ratios and lignin contents of 15-25 wt%. At lignin contents of 30 wt% or above, hard and brittle films were obtained irrespective of the NCO/OH ratio employed. Hard and glassy polyurethanes were produced at NCO/OH ratios of 1.8 or greater which were not testable.