Oil palm trunk (OPT) contains a considerable amount of starch. The starch-rich powder was separated from the fiber of OPT by dry-method and was found to be fermentable. Lactic acid (LA) is an important chemical due to its various applications such as in food, pharmaceutical, textile, leather, cosmetic and chemical industries, and the market demand is increasing. In this study, OPT starch was hydrolyzed by using commercial α–amylase (Liquozyme Supra) and glucoamylase (Dextrozyme DX) from NOVOZYMES A/S. Then, the process was continued with LA fermentation. Several strains of LA bacteria were tested for the ability to convert the sugar to lactic acid. The fermentation resulted in Lactobacillus plantarum performing the highest yield of LA. An effort to obtain higher LA productivity of L. plantarum, the effect of the addition of calcium carbonate (CaCO3) on the lactic acid production was studied. The CaCO3 was added 8 h after the fermentation started. The highest lactic acid concentration 90 g/L was achieved at 48 h by addition of 3% CaCO3 on hydrolyzed OPT starch medium fermentation which contained 100 g/L glucose (productivity was 1.87 g/L/h). [ABSTRACT FROM AUTHOR]