White spot syndrome virus(WSSV) , a non-occluded virus which is the causat ive agent of a disease caused high shrimp mortalities and severe damage to shrimp cultures, was iso lated and purified. Virions are rod-shaped, enveloped, 430nm @ 120nm in size, with a tai-l like appendage at one extremity. Nucleocapsids are 300nm @ 85nm in size, and are composed of rings of subunits in a stacked series. The genome of the virus is a double-stranded DNA molecule. The full length of the DNA is estimated to be longer than 165kb. EcoR . or Sal . restriction fragents obtained after agarose gel electrophoreses were cloned in the system pBluescript ò KS-XL1-blue. Southern hybridization, dot blot hybridization and in situ hybridizat ion were performed using the WSSV EcoR . clone fragments as probe, and those proved that these clone fragments are specific to WSSV. According to the results of nucleotide sequence analysis, none of the WSSV clones showed considerable se- quence homology with those of other known viruses or organisms, indicating that WSSV may only be distantly related to baculoviruses.