Three filamentous fungal strains were isolated form Carassius auratus eggs with Saprolegniasis, and strain JL1 was proved to be pathogenic to Carassius auratus eggs by artificial infection. Therefore, morphology and growth characteristics of strain JL1 were studied, and the phylogenetic analysis based on its ITS rDNA sequence was further conducted. The experimental results showed that the hyphae of strain JL1 was aseptate, transparent and seldom branched. Its zoosporangia were often clavate and renewed internally. Primary zoospore was multi-row arrangement in zoosporangia and discharged in Saprolegnia fashion. Spherical oogonia was attached by monoclinous or diclinous antheridium hyphae. The ITS rDNA sequences of strain JL1 was naturally clustered with ITS rDNA sequences of Saprolegnia sp. submitted to GenBank with 99% of homology, and had closest relationship with Saprolegnia sp. H (accession number: EF460351). Combined morphological characterization with phylogenetic analysis based on ITS rDNA sequence, strain JL1 was identified as Saprolegnia sp.. In addition, strain JL1 could grow at 5 °C?30 °C and pH 4?11, its optimum growing temperature and pH were 25 °C?30 °C and 6?9, respectively. Strain JL1 was sensitive to sodium chloride, its growth could be completely inhibited by 2% NaCl, which could serve as a foundation for the Saprolegniasis control.