The study of bioproduct production, such as bioethanol and biochemicals, from inexpensive biomass has recently attracted considerable attention. Compared to land biomass, marine biomass can be grown rapidly and is easily cultivated without the need for expensive equipment. In addition, annual CO2 absorption by marine biomass is five to seven times higher than that of wood-biomass and the carbohydrate content is higher and can easily be converted to chemicals through proper chemical processes. In the production of various biochemicals from marine biomass, levulinic acid is a highly versatile chemical with numerous industrial uses and the potential to become a commodity chemical. It can be used as a raw material for resins, plasticizers, textiles, animal feed, coatings and antifreeze. The present study was carried out to determine the optimum conditions of temperature, acid concentration and reaction time for levulinic acid production from marine biomass Gelidium amansii using two-step treatment. In the first hydrolysis step, solid-state cellulose was obtained through acid soaking and used to produce ethanol by fermentation and liquid-state galactose. In the second hydrolysis step, the liquid-state galactose was converted into levulinic acid via a high-temperature reaction in a batch reactor. The overall production conversion of G. amansii biomass to levulinic acid in the two-step acid hydrolysis was approximately 20.6%. (C) 2012 Elsevier Ltd. All rights reserved.