The aim of this study was to detect the expression pattern of DNA methyltransferase 3B (DNMT3B) variants in primary gastric cancer (GC) and to explore the clinical significance of DNMT3B variants in gastric carcinogenesis. Specific polymerase chain reaction (PCR) primer sets were designed to distinguish individual DNMT3B variants according to their splicing patterns. Expression levels of DNMT3B variants were assessed by quantitative real-time RT-PCR in gastric cancer tissue, normal gastric mucosae and GC cell lines. The relationship between the expression patterns of the DNMT3B variants and corresponding clinical information was analyzed by observing the expression levels of different variants in the tumors. These results demonstrate that DNMT3B overexpression is related to late phase invasion (P=0.029) and intestinal type (P=0.012) in GC. DNMT3B3 expression was higher in normal tissue, compared to tumor tissue (P=0.033). In contrast, only 18, 32 and 35% of the patient tumors overexpressed DNMT3B1, DNMT3B4 and DNMT3B5, respectively. While taking into account environmental factors (H. pylori, Epstein-Barr virus infection), H. pylori infection elevated DNMT3B1 and DNMT3B3 variants in tumors, while increasing DNMT3B4 in both tumor and non-cancerous tissues. Our findings indicated that the expression of DNMT3B3 is the major splice variant in normal gastric mucosae and may be affected by H. pylori infection. Elevated DNMT3B variants may influence the progression of gastric cancer and may possibly be a powerful indicator for the disease.