The samples including blood, lung, pulmonary lymphnode, heart, liver, spleen, kidney from pigs infected with porcine reproductive and respiratory syndrome (PRRS) virus were used for isolation of PRRS virus on Marc 145 cell line. Marc 145 cell are suitable to isolate PRRS virus. Virus quickly replicated in cells and causing typical lesions as: cells clustered and shooting up the bottoms of jars. PRRS caused cytopathogenic effect (CPE) in Marc 145 cells as early as 36 hour post inoculation
from 84 hour post inoculation to 108 hour post inoculation, cells were peeled from cultural surface. Titer of virus isolated from samples is determined minimum at 3.16 x 10 exponent 2 (TCID50/25 ul) and maximum at 6.67 x 10 exponent 4 (TCID50/25 ul). Released virus's titer was higher than cell associated virus's titer. The cell associated virus's titer of isolated virus increased continuosly after 48 hour post inoculation, maximum at value log TCID50 = 4.83. This research compared a number of biological characteristics about causing CPE, virus's titer, rule of viral replication PRRS isolated virus with strain virus vaccine. This research helped to diagnosis by selecting PRRS strain virus to manufacture vaccine and antigen.