Abstract: A root rot disease of pines was found lor the first time in about ten-year-old Pinus ell-iottii stands in the Leizhou Penisula oi Guangcong l rovince of China. Field survey and inoculation tests provided convincing evidence that P p od a n en was the primary pathogen of the disease,and Botryodiplodia theobromae also a pathogen of P. e p P aeda and P.caribaea.Inoculation tests indicated that the pathogencity of D.pirea varted among different s-pecies of pines. Pinus elliottii was more susceptible to attack by D. pirea than P.taeba and P. caribaea, and that P. massoniana was resistant.The mycelia of D.pinea could survive lor more than 150 days in infected roots of P. elliottii under natural conditions, and for 120 days in natural soil of different water contents, when soil moisture was 5%, 15%, 25%, 50%,conidia could also survive for more than 120 days in natural soil. These results indicated that D.pinea was likely a soil-borne fungus.The infection of P.pinea was also related to water content, Low water content was favourable to infection by the fungus. When the water content was below 50%, D. pinea attacked lateral root section easily;wben the water content was above 50%, it was difficult for the fungus to attack. Soil moisture may also influence the occurrence and development of the disease. Lower water content lasting for 20 days could make P.elliottii seedlings more susceptible to the disease.