Abstract: Objective To explore the effect of prophylactic dexamethasone on postoperative cognitive function after plasmakinetic enucleation of the prostate. Methods A total of 100 aged patients treated with plasmakinetic enucleation of the prostateunder general anesthesia were randomized to dexamethasone group(n=50)and control group(n=50), given intravenous injection of 0.1 mg/kg dexamethasone at 2 h before surgery, and the same dosage of normal saline respectively. The cognitive function scores of the two groups were measured by Mini Mental State Examination Scale(MMSE)at the first day before operation and at 1, 3, 7 d after operation, and the levels of interleukin-6(IL-6), tumor necrosis factor -α(TNF-α), C reactive protein(CRP)were measured. Results Compared to the control group, the dexamethasone group showed significant reduction in the incidence of postoperative cognitive dysfunction, and IL-6, TNF-α and CRP levels at 1^st, 3^rd postoperative day in the dexamethasone group(P<0.05). Conclusion Preoperative administration of dexamethasone can reduce the inflammatory response and decrease early risk of postoperative cognitive dysfunction after plasma kinetic enucleation of the prostate.