A new bacterial isolate， Paenibacillus sp. OSY-N， showed potent antimicrobial activity against Gram-negative and Gram-positive bacteria. Antimicrobials produced by this strain were purified by reverse-phase high-performance liquid chromatography. Structural analysis， using mass spectrometry， of a single active HPLC fraction revealed two known cyclic lipopeptides (BMY-28160 and permetin A)， a new cyclic lipopeptide， and the linear counterparts of these cyclic compounds. The latter were designated as paenipeptins A， B and C， respectively. The paenipeptins have not been reported before as naturally occurring products. Paenipeptins B and C differ at the acyl side chain; paenipeptin C contains a C8-， instead of C7-fatty acyl side chain. To demonstrate unequivocally the antimicrobial activity of the linear forms of this family of cyclic lipopeptides， analogs of the paenipeptins were synthesized chemically and their antimicrobial activity was tested individually. The synthetic linear lipopeptide with an octanoic acid side chain (designated as paenipeptin C΄) showed potent antimicrobial activity with minimum inhibitory concentrations of 0.5-4.0 μg/mL for Gram-negative and 0.5-32 μg/mL for Gram-positive bacteria. Findings demonstrated that peptide cyclization in this lipopeptide family is not essential for their antimicrobial activity. Most importantly， linear lipopeptides are more accessible than their cyclic counterparts through chemical synthesis.