Lactic acid (2-hydroxypropionic, CH3CHOHCOOH) is the most widely utilized organic acid in the food, pharmaceutical, cosmetics and chemical industries. Its production is currently attracting a great deal of research and development. Lactic acid exists naturally in two optical isomers: d(?)- lactic acid and l(+)-lactic acid. Since elevated levels of the d-isomer are harmful to humans, l(+)-lactic acid is the preferred isomer for food-related and pharmaceutical industries. Lactic acid can be produced commercially by either chemical synthesis or fermentation. The chemical synthesis results in a racemic mixture of the two isomers, while the fermentation process can yield an optically pure form of lactic acid or racemate, depending on microorganisms, substrates and fermentation conditions employed in the production process. Renewable resources including sugars, starch and lignocellulose are abundant substrates for fermentative production. The most commonly used synthetic method for chemical production of lactic acid is the hydrolysis of lactonitrile derived from acetaldehyde and hydrogen cyanide, which are produced by petrochemical process. Therefore, chemical synthesis may be limited due to a shortage of the naturally available raw materials in the future. Lactic acid can be produced using bacteria and fungi. Lactic acid producing bacteria (LAB) have received wide interest because of their high growth rate and product yield. This expensive downstream process increases the overall cost of production of lactic acid using lactic acid producing bacteria. Fungal Rhizopus species have attracted a great interest, and have been recognized as suitable candidates for lactic acid production. Unlike the LAB, lactic acid producing Rhizopus strains generate l-lactic acid as a sole isomer of lactic acid. In the second of 20 th century, lactic acid knew as the component of metabolism and common material of various industries like pharmaceutical industry, food industry, leather industry and medical industry to prepare medical instrument. lactic acid (L+) is prevalent in food and pharmaceutical industries while lactic acid (D-) is used in leather and textile industries. Furthermore, the type of polymer of lactic acid (PLA) is applied in clinic cases and also to manufacture medical instrument. The main resources to produce lactic acid are sugars, starch, and lignocellulosic materials. In this project, production of lactic acid from pine wood by fermentation was investigated. The wood was pretreated, enzymatically hydrolyzed, and fermented by two different fungi. Similar to other lignocellulosic materials, the wood composed of three major groups of polymers, i.e. cellulose (polymer of glucose), hemicelluloses (polymer of pentose and hexose sugars) and lignin. Concentrated phosphoric acid pretreatment at modest reaction conditions and alkaline pretreatment by NaOH were used. Then the pretreated pine woods were subjected to enzymatic hydrolysis using commercial cellulase and ?-glucosidase enzymes. The hydrolyzates were then fermented by Rhizopus fungi. Untreated pine wood without any pretreatment was also hydrolyzed by the enzymes and then fermented. The analysis of the treated woods showed the maximum glucan yield of 43% by alkaline pretreatment, where as the treatment with phosphoric acid resulted in a substrate with 40% glucan. Thus, both of the treatment resulted in higher glucan substrate compared to the untreated wood, which contain 35% glucan. The enzymatic hydrolysis of phosphoric acid and alkaline pretreated wood resulted in 46 and 19% glucose yields, respectively, which was higher than that for untreated wood (6%). Fermentation of the hydrolyzates resulted in 326 grams lactic acid per kg of glucose that can be produced from the phosphoric acid pretreated substrate by Rhizopus oryzae . This value was 151g/kg for the alkaline pretreated substrate. Fermentation of the acid and alkali treated substrates by R. microsporus resulted in 122 and 39 grams lactic acid per kg glucose, respectively. Keywords : Lactic acid, pine wood, Rhizopus , pretreatment, enzymatic hydrolysis, fermentation.