| A quantitative method based on LC-MS was established for detection of compounds involved in the biosynthetic pathway of jasmonic acid and to detect the changes of these compounds in Gracilariopsis lemaneiformis and Pyropia haitanensis when they were subjected to mechanical damage. Jasmonic acid (JA), methyl jasmonate, 12-oxy-phytodienoic acid and 13-hydroperoxylinolenic acid (13-HpOTE) were extracted with 100% methanol, and the four compounds were separated by XBridgeTM C18 chromatographic column with methanol/water as mobile phase. The results showed that the four compounds could be separated well under optimal conditions. The recoveries of the four compounds were 81.23-90.25%, and the detection limits of the method were between 0.04 and 0.56 ng/mL, indicating that the high sensitivity of this method. These four compounds in G. lemaneiformis, Pyropia haitanensis and Gracilaria asiatica were analyzed. In addition to no JA and 13-HpOTE detected in P. haitanensis, four compounds were detected in the other two species of red algae. The content changes of these compounds in G. lemaneiformis under mechanical damage stress were analyzed, and it was found that when the alga was stressed, the contents of them were accumulated within a short time, and the responses of them were rapid. After P. haitanensis was mechanical damaged, JA production was detected, but the response rates of these compounds were slower than G. lemaneiformis. These results suggest that some red algae may have a similar pathway of jasmonic acid synthesis to that of plants, and also may participate in the stress response to mechanical injury.