Abstract: Objective:To detect A 20mutation and to investigate its relationship with clinicopathologic features, prognosis, and re-sistance to therapy of diffuse large B cell lymphoma (DLBCL). Methods:A total of 104 cases with DLBCL and their clinical data were collected; follow-up was performed on a few of DLBCL patients. The expression of P-gP and Ki-67protein was detected with immuno -histochemical staining. The A 20gene mutation in exons 3, 6, and 7 were examined by polymerase chain reaction and DNA sequencing. Finally, the correlation of genetic abnormality of A 20with clinicopathologic features was analyzed. Results: Missense mutation in ex -on3 of A 20gene was identified in 18of 104 patients ( 17.3%). The A20gene mutation at site 73of exon3 was greater in the cases with activated B cell-like-DLBCL than with germinal center B-cell-like-DLBCL ( 18.5% vs . 2.5%,P=0.010). In contrast to the advanced clin -ical stage and high International Prognostic Index (IPI) cases, the rate of A 20mutation was superior to the opposite ( P<0.05). The ex -pression for P-gP was higher in the cases with mutation than that of those with wild-type A 20gene (16/18vs . 52/86, P=0.021). The dif -ference in A20mutation between the groups of low and high positive expression for Ki- 67(1/17vs . 26/60, P=0.030) was significant. DLBCL with A20mutation had an increasing recurrence tendency (P=0.06) and a worse survival ( P=0.016) compared with those with wild-type A 20gene.Conclusion:The A20mutation has a certain influence on the clinicopathologic characteristics and survival condi-tions of BLBCL patients. Probably, A20mutation is a factor associated with a poor prognosis of DLBCL.