Abstract: 3% sumithion was sprayed twice by a plane over the forest around Dr. Sun Yatsen’s Mausoleum, Nanjing in 1987 to control Bursaphelenchus xylophilus. The total areas were 10800 mu and 11400 mu respectively. The use of sumithion was once criticised because of the environmental pollution caused and the harm to man and animals done by it. So the dynamic of sumithion residues in the forest around Dr. Sun Yatsen’s Mausoleum was studied by collecting samples for determination at different time after spray. It turned out that the residues in samples Ⅰ-Ⅳ had been degraded below 0.5 ppm with very few except-ations 7-15 days later after the spray. This amount is much lower than that one lawfully permitted by European Economic Community. No injury was found to the plants and no abnormal phenomena to the birds during the seven days after the spray.