Colistin has been regarded as the last line antibiotic for treatment of infections caused by multidrug resistant gram-neg. bacteria. Therefore, the increasing emergence of colistin resistance among gram-neg. bacteria represents a serious problem. The objective of this study was to characterize the effectiveness of the chem. synthesized thanatin in linear form against colistin-resistant E. coli isolated from a pig farm in China. Agar diffusion assay and broth microdilution test were employed to analyze the susceptibility of colistin-sensitive E. coli (ATCC25922) and colistin-resistant E. coli (SHP45) to linear thanatin (L-thanatin). Combinatory effect of linear thanatin and colistin against E. coli was also determined by fractional inhibition concentration index (FICI) anal. The results showed that L-thanatin at a concentration of 1 mg/mL produced larger inhibition zone on agar against ATCC25922 than SHP45. In the quant. microdilution test, L-thanatin had the same MIC of 3.2 μg/mL for ATCC25922 and SHP45. Based on the FICI anal., additive effect was obtained with 1.56 μg/mL of L-thanatin and 0.125 μg/mL of colistin for ATCC25922; but with 1.56 μg/mL of L-thanatin and 0.25 μg/mL of colistin or with 2 μg/mL of colistin and 0.39 μg/mL of L-thanatin for SHP45. These data proved that L-thanatin is an effective antimicrobial peptide against colistin-resistant E. coli.