To compare the effects of polysaccharide nucleic acid fraction of bacillus calmette guerin (BCG-PSN) and thymopeptides on T-lymphocytes of normal and immunosuppressed mice, CD4+ and CD8+ T-lymphocyte subsets of single nucleic cell in thymus, spleen and peripheral blood were detected successively by flow cytometry after application of BCG-PSN and thymopeptides. Meanwhile, CD4+/CD8+ ratio was also calculated. The results showed that both BCG-PSN and thymopeptides could decrease the proportion of CD4+ CD8+ T-lymphocyte subsets in the thymus, at the same time increase CD4+ T-lymphocyte, CD8+ T-lymphocyte proportion in the three tissues.The fluctuation in amplitude was greater in thymopeptides group than that in BCG-PSN group. It is concluded that acting location of thymopeptides is in thymus, its stimulating action is stronger than that of BCG-PSN, while BCG-PSN not only accelerates the differentiation in thymus, but also has some direct stimulation to peripheral CD4+ T-lymphocytes, and can maintain CD4+/CD8+ ratio within normal range. So, BCG-PSN is safer.