Objective To understand the relationship between tumor necrotic factor α (TNF α) and brain damage in an animal model of pertussis bacilli induced brain edema. Methods 99 rats were divided into 3 groups: 1)sham control group (C group, n=11); 2)normal saline group (NS group, n=44); and 3) pertussis bacilli group (PB group, n=44). TNF α mRNA expression was examined using RT PCR and the protein levels were assayed using ELISA in the rat brain tissues at various times. Results TNF α was significantly increased in the PB group at 240 min ( 768.4 ± 86.3 pg/g) compared to the C group ( 318.1± 31.1 pg/g), NS group at 30 min ( 324.2 ± 65.6 pg/g), NS group at 60 min ( 322.1± 73.4 pg/g), NS group at 120 min ( 316.8 ± 49.1 pg/g), and NS group at 240 min ( 329.9 ± 77.6 pg/g). The PB group at 240 minutes was also significantly increased compared to the PB group at 30 min ( 360.3 ± 66.6 pg/g), at 60 min ( 358.5 ± 49.1 pg/g), and at 120 min ( 356.0 ± 52.3 pg/g) (P< 0.01 ). Expression of TNF α mRNA began to increase in the PB group at 60 min and reached a peak at 240 min. Conclusions TNF α may play a role in producing injury in infectious brain edema.