In order to study the effects of phosphorothioated antisense oligodeoxynucleotides (ASODN) on the expression of VEGF in human lymphoma cell line Namalwa cells, human lymphoma cell line Namalwa cells were incubated with VEGF ASODN (the final concentrations of VEGF ASODN were 5, 10, 20 micromol/L respectively), or scrambled sequence for 24 or 48 hours. The expressions of VEGF mRNA and VEGF protein were detected by reverse transcriptase-polymerase chain reaction and streptavidin peroxidase (SP) immunohistochemistry respectively. The results showed that the expression levels of VEGF mRNA in Namalwa cells treated with three concentration levels (5, 10, 20 micromol/L of ASODN) were 1.38, 0.96 and 0.57 respectively. Those in PBS-treated cells and scrambled sequence treated cells were 1.79 and 1.84. When treated with 20 micromol/L VEGF ASODN for 48 hours, VEGF protein of Namalwa cells decreased greatly. Meanwhile, there was no obvious change in the scrambled sequence treated group. It is concluded that VEGF ASODN can suppress the VEGF expression in Namalwa cells in vitro.