Abstract: Objective：To evaluate the important role of Cefepime as empiric antibiotic therapy on aged patients with severe hospital acquired pneumonia （SHAP）.Methods：115patients with SHAP，receiving no prior antibiotic therapy，were divided into two groups： Cefepime （CFP） group and Imipenem/cilastatin （IMP） group.the clinical efficacy and the bacteriological characteristic were analyzed in both groups.Results：①there was no statistical significant difference in clinical efficacy between CFP group （86.4%，the effective rate） and IMP group （89.3%，the effective rate），P=0.641.②The occurrence rate of bacteria in the sputum was 91.5% in CFP group and 91.7% in IMP group，with a predominance of Gram-negative bacilli in the two groups （80.5% vs 85.7%）.Pseudomonas aeruginosa，Acinetobacter，Enterobacter cloacae，Klebsiella pneumoniae and Staphylococcus epidermidis were the major pathogens in both groups，and showed the similar susceptibility to Cefepime and Imipenem/cilastatin.③The bacteriological effective rate was 88.9% in CFP group and 88% in IMP group （P=0.916），and the bacteriological clearance rates were 89.6% and 91.4% （P=0.708） respectively. ④There were 7isolates of Candida（12.5%） and 3isolates of Stenotrophomonas maltophilia （5.4%） in IMP group after treating，but nothing in CFP group，P=0.005.⑤The effectiveness/cost ratio was 0.137‰ in CFP group and 0.127‰ in IMP group （P＞0.05）.Conclusion：Cefepime，with antibacterial spectrum，antibiotic activity and clinical efficacy similar to Imipenem/cilastatin， could be used as the idea single drug to empirically treat the aged patients with SHAP.