In this study, Alcell lignin was used as filler in aliphatic urethane acrylate ultra violet (UV) curable resin system. The coating system was UV cured in the presence of free radical photoinitiator and cationic photoinitiator. The results showed that those with free radical photoinitiator produced coating film with higher degree of curing than those with cationic photoinitiator. The result of iodine number determination also showed that the unsaturated groups present in the UV curable system had reduced. This indicated that radical polymerization had taken place in the curing process of UV curable resin incorporated with lignin. In addition, the lignin content did not influence the curing process of the coating film. As for the coating film, it showed that the mechanical properties of the film were significantly influenced by the lignin content. This phenomenon was contributed by inherent stiffness of the lignin. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2527-2533, 2011