Abstract: It expression increase from the later G phase.through the S phase of cell cycle. Glial fibrilary acidic protein(GFAP) as a intermediate filament protein, representing glial fibrils inside the tumour cells, is a marker for astrocytomas differentiation. In 40 cases of,astrocytomas ABC immunohistochemical method is applied to examine the expression of PCNA and GFAP. the results showed that the positive ratio of the expression of PCNA and GFAP have significant stepwise increased(P0.01)and decreased (P0.01) in the tumour classifications, respectively. There is a negative correlation between the degrees of expression of PCNA and that of GFAP. It is suggested that the quantifications of PCNA and GFAP represents a potentially useful tool for the studies of the proliferative activity, malignant degrees and cellular differentiation in astrocytomas.