In 2004 and 2005, Phytophthora rot on Luffa cylindrica which had not been reported in Korea occurred in the experimental field at Gyeongsangnam-do Agricultural Research and Extension Services. The disease initiated on leaves and fruits of the plant with small watersoaked dark brown spots and progressed rapidly. The causal pathogen isolated from diseased tissues was identified as a Phytophthora sp. because of aseptate mycelia and zoospores released directly from sporangia. The fungus grew well on PDA and 10% V-8 juice agar showing an arachnoid or rosaceous colony pattern. Sporangia formed abundantly in water and were conspicuously papillate, noncaducous, ovoid to globose, and sized 26~62×19~38 μm. The fungus was heterothallic as producing sexual reproduction structures only when mated with only A2 standard mating type strain. Oogonia and oospores were spherical, smooth walled, and measured as 20~28 μm and 16~24 μm, respectively. Oospores were aplerotic and antheridia were amphigynous, unicellula and spherical. Chlamydospores were globose and 20~38 μm in diameter. Optimum temperature for growth was around 28~30oC. The fungus caused similar symptoms on artificially inoculated plant and could be re-isolated thereby proving Koch`s postulation. Based on the mycological criteria investigated in this study, the causal fungus of Luffa sylindrica rot was identified as Phytophthora nicotianae. This is the first report of Phytophthora rot of Luffa cylindrica caused by P. nicotianae in Korea.