Transesterification of high free fatty acid content Jatropha oil with methanol to biodiesel catalyzed directly by NaOH and high-concentrated H2SO4 or by two-step process were studied in an ultrasonic reactor at 60 C. If NaOH was used as catalyst, biodiesel yield was only 47.2% with saponification problem. With H2SO4 as catalyst, biodiesel yield was increased to 92.8%. However, longer reaction time (4 h) was needed and the biodiesel was not stable. A two-step, acid-esterification and base-transesterification process was further used for biodiesel production. It was found that after the first-step pretreatment with H2SO4 for 1 h, the acid value offatropha oil was reduced from 10.45 to 1.2 mg KOH/g, and subsequently, NaOH was used for the second-step transesterification. Stable and clear yellowish biodiesel was obtained with 96.4% yield after reaction for 0.5 h. The total production time was only 1.5 h that is just half of the previous reported. The two-step process with ultrasonic radiation is effective and time-saving for biodiesel production from Jatropha oil. (C) 2010 Elsevier Ltd. All rights reserved.