Objective To detect the expression of β-catenin in the tissues of primary central nervous system lymphoma (PCNSL), and to discuss its function in PCNSL.Methods The paraffin embedded tissues from 10 patients diagnosed as PCNSL from October 2010 to April 2012 were collected as the experimental group.The paraffin embedded tissues from 10 patients with lymphadenitis were collected as the control group.Quantitative real-time PCR and immunohistochemical method were used to detect the expression of β-catenin in these tissues, and the relationships between β-catenin and clinical data were analyzed.Results Immunohistochemistry results showed that β-catenin protein was localized in the cytoplasm and (or) nucleus.Among 10 PCNSL patients, β-catenin protein was positive in 4 patients, while it was no positive in all of 10 lymphadenitis patients, with the significant differences between both groups (P ＜ 0.05).The β-catenin gene relative expression level was 4.70±0.57 and 1.00±0.27 in the experimental group and the control group, respectively.β-catenin expression was no correlation to age, PS score, cerebrospinal fluid protein level and serum lactate dehydrogenase level of patients with PCNSL.Conclusions Whether in mRNA level or in protein level, β-catenin expression is always high in PCNSL tissues, and its protein is expressed in the cytoplasm, however, this phenomenon was not observed in the tissue of lymphadenitis.