Abstract: The test was conducted with 8-year-old trees of longan cultivar“Wulongling”.Fruit clusters were sprayed with the simulated acid rain with different pH values to study the effects of the acid rain on the polyamine contents in young fruits of longan.The results show that the contents of polyamines(PAs),putrescine(Put)and spermidine(Spd)+spermine(Spm) increase under the stress of acid rain.This is a prompt response to the acid rain stress which can last for a longer period.With the development of young fruits,their contents decrease.The contents of PAs,Put,Spd+Spm in the easily-dropping fruit are significantly higher than those of formal ones.