Abstract: Oligochitosan prepared by enzymatic hydrolysis of chitosan is a potent plant defense elicitor, but the mechanism of oligochitosan inducing resistance of plants to pathogens is still unclear. In this study, we applied different concentrations of oligochitosan to tobacco suspension cells to investigate the change in gene expression involved in jasmonic acid biosynthesis.Semi-quantitative RT-PCR revealed that 50 μg.mL-1 oligochitosan up-regulated the expression of genes encoding phospholipase A2,13-lipoxygenase, allene oxide synthase, allene oxide cyclas e and 12-oxo-phytodienoic acid reductase in a similar manner. The gene expression of phospholipase A2 was increased over time, whereas increased expression of the other genes appeared at 8 h after treatment. These results showed that the jasmonic acid biosynthesis pathway can be triggered by 50 μg.mL-1, rather than 200 μg.mL-1, oligochisan suggesting that the action of oligochitosan in tobacco suspension cells was dose dependent, and that a higher concentration of oligochitosan may activate a defense res ponse without the participation of jasmonic acid.