Abstract:Physiological fruit drop of longan (Dimocarpus longan Lour. cv. Shuizhang) wasstudied by measuring the cellulase and pectinase activities and ABA content in juvenile fruitscollected from 5 trees of 15 years old in Fujian Province in May 1993. The results showedthat there was a significant relationship between cellulase activity and fruit dropping.Cellulase activity in drop fruits was significantly higher than that in normal ones. No obvi- ous difference in pectinase activity‘ between normal and drop fruits was found, and thepectinase activity was slightly enhanced in drop fruits only at middle stage of fruitdropping. The content of ABA in drop fruits was higher than that in normal fruits. It wasshown that higher content of ABA and higher cellulase activity promote-d physiological dropof longan juvenile fruits.