Objective To investigate the protective mec,hanism of soybean isoflavones ( SIF) against the inflammatory impairment in the brain of rats induced by [3-amyloid peptidel-42 (A[31-42). Methods Based on the body weight of rats, 32 healthy Wistar rats ( male, aged 3 months) were randomly divided into four groups ( control, A[3, SIF +A[3 and SIF groups). The inflammatory impairment model was established by injecting A[3142 (10肛g) into the lateral cerebral ve,ntricle of rats with micropump for 14 days. The rats in SIF + A[3 and SIF groups were treatecl with SIF ( 80 mg/kg bw) per day by gavaging for 14 days before the injection of A[3, while the rats in control group and A[3 group were treated with 0.5 % CMC-Na. On the 15'h day after A[3 injection, the rats were killed for the mRNA and protein expression of interleukin-1[3 ( 11-1 [3) , inducible nitric oxide synthase ( iNOS) and interleukin-10 ( IL-10) in brain tissue tested hy RT- PCR and western blot. Results Comparing with the A[3 group, the mRNA and protein expression of IL-1[3, iNOS and IL- 10 0f SIF treated groups were decreased significantly ( P < 0. 05). Conclusion The expression of IL-1[3, iNOS ancl IL-10 at gene and peotein level could be down-regulated by soy isoflavones, therefore the inflammatory damage induc:ed by A[31- 42 was inhibitd.