In this study, we employed time-resolved synchrotron SAXS for label-free structural measurements to assess the permeability kinetics of monoatomic ions within milliseconds. Using large unilamellar vesicles (LUVs) with zwitterionic and anionic lipids mimicking the E. coli membrane charge, we examined three natural AMPs: indolicidin, LL-37, and aurein. LUVs in a salt-free buffer at physiological pH were subjected to osmotic shock by mixing with NaCl, creating a hypertonic environment that deformed the vesicles. However, vesicles pre-incubated with AMPs did not deform, even at high salt levels, indicating permeabilization. Additionally, the peptide partitioning was unaffected by salt concentrations, and no membrane solubilization occurred. Using time-resolved SAXS (TR-SAXS) combined with a stopped-flow apparatus (SFA), we tracked the rapid ion transport across the lipid membranes with millisecond resolution. Indolicidin achieved salt equilibration in less than 0.10 seconds, LL-37 at a 1:100 PL ratio equilibrated in 0.34 seconds, and aurein facilitated equilibration within the minimum delay time of 7.8 milliseconds. These results suggest that structural pores are not necessary for rapid ion transport. Based on previous atomistic MD simulations , we estimated the diffusion coefficient of Na + through for membranes incubated with indolicidin. By employing a theoretical diffusion model based on transient water channels, we demonstrated that even a few short-lived transient pores can account for the observed permeability.