Abstract: After the isolate of Lecanosticta acicola was seperatly cultured in wheat solid medium and potato dextrose liquid medium for 30 days, the water extract and the filrate of the cultures could quickly make the needles of slash pine, masson pine and Japanese black pine lose green, and the seedlings of tomato and tobacco get wilt in vitro. It was suggested that the pathogen could yield and secrete the toxic substance and the toxin was probably an important way in the pathogenisis of L. acicola. The toxin had no host specificity. The filtrate or the extract was isolated into two parts, the protein part and the non protein part. The test showed that the toxic part was non protein. The toxic non protein part was further isolated into 3～4 parts in each of three different solution system, and there was always a part of each system which could show toxinicity. To the toxin the slash pine needles were high sensitive, the masson pine needles medium sensitive, and the Japanese black pine needles comparatively lower sensitive.