This experiment was conducted to study the synergistic effects of antimicrobial peptides and antibiotics against Gram-negative and Gram-positive bacteria in vitro. A synergistic bactericidal effect was observed when combinations of LFcin B, Cecropin A, aureomycin and neomycin were used against Escherichia coli ATCC25922, Staphylococcus aureus ATCC25923, Salmonella choleraesuis CMCC50013, and Pseudomonas aeruginosa CMCC10014, using microbroth dilution method. The combination study showed synergy between LFcin B and Cecropin A, as well as LFcin B and aureomycin. In addition, Cecropin A was shown to be synergic with aureomycin. These results indicate that a synergistic effect exists when antimicrobial peptides and antibiotics were used in combination against Gram-negative and Gram-positive bacteria.［Chinese Journal of Animal Nutrition, 2010，22（5）:1457-1463］