Abstract. The aims of the present study were to elucidate the transcript levels of DNA methyltransferase (DNMT)1, DNMT3a and DNMT3b by quantitative polymerase chain reaction in patients with primary gastrointestinal diffuse large B-cell lymphoma (PGI-DLBCL), and determine the association of their expression with the clinical parameters and prognostic values of the disease. The results revealed that the expression of DNMT1 in patients with PGI-DLBCL was significantly higher than that in healthy controls (P=0.04), while the expression of DNMT3a and DNMT3b were significantly lower (P<0.001 and P=0.001, respectively). The increased expression of DNMT1 was significantly correlated with shorter overall survival and progression-free survival rates (P=0.018 and P=0.008, respectively). The multivariate analysis demonstrated that the level of DNMT1 was an independent prognostic factor. In conclusion, DNMT1 was identified to be an independent prognostic factor for predicting the survival of patients with PGI-DLBCL; this suggests that it could be used as a marker to indicate the prognosis of PGI-DLBCL.