To study the correlation between 50% tissue-culture infective dose (TCID50) value and p27 antigen S/P value of Avian leukosis virus subgroup J and discuss their significance, chicken embryo fibroblast (CEF) cells were inoculated with Avian leukosis virus subgroup J strain NX0101 and samples were tested continuously for ten days after changing maintenance media. The correlation between TCID50 and p27 antigen S/P value of ten days were then analysized. Simultaneously, DF-1 cells were inoculated with NX0101 and passaged to 20 generations. Samples taken from 1st generation, 5th generation, 10th generation, 15th generation and 20th generation were tested for the TCID50 titer and the p27 antigen S/P value separately. A significant Pearson correlation was found between them in CEF cells (r = 0.85277; P < 0.0001) and in DF-1 cells (r = 0.93000; P = 0.0220). This study provided an important parameter for predicting TCID50 by detecting the p27 antigen S/P value.