The germination and infection of conidia of brown spot needle blight fungus (Lecanosticta acicola) on pine needles were observed under scanning electron microscope (SEM). Results showed that the conidia on the needles of Pinus massoniana, P. elliottii and P. thunbergii all germinated in the same way, and their germ tubes invaded into the needles through stomata, mostly 3-4 days after inoculation. Tests indicated that the peroxidase activity in needles of the resistant host P. Massoniana, increased rapidly 5 days after inoculation, but there were no evident changes of such activity in the needles of the susceptible hosts P. elliottii and P. thunbergii. There were no prominent relations between the peroxidase activity levels and disease resistance in all these three species of pines. The levels of peroxidase activity in needles of different individuals of P. elliottii also did not reflect their corresponding susceptibilities.