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Background: Levofloxacin has been widely used as a quinolone antibiotic with a broad spectrum of action against gram-positive, gram-negative, and anaerobic bacteria. However, this drug has a short half-life in vivo and has to be frequently administered. Objective: In this study, we aimed to prepare electrolyte microcomplexes (EMCs) exhibiting high encapsulation efficiency and modified release profile using electrostatic interaction between levofloxacin (LFX) and lambda-carrageenan (LCN). Materials and Methods: EMCs were prepared using an ultrasonic disperser at the various ratios of LFX:LCN (1:0.5, 1:1, 1:3, w/w) and pH conditions (pH 2.0 - pH 5.0). EMCs were investigated in terms of mean particle size, encapsulation efficiency, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and in vitro dissolution. Results: With an increase of the ratio of polymer, the particle size decreased, and the encapsulation efficiency increased. EMCs prepared at the ratio of LFX:LCN = 1:3 (w/w) showed a mean particle size of less than 3 ㎛ and the highest loading efficiency (90.78 ± 0.05%). Electrostatic interaction between the piperazine ring (2802 ) from LFX and sulfate group (1215 ) from LCN was confirmed in the FT-IR spectrum. EMC was changed in the morphology compared to powder LFX and LCN. In the dissolution test, EMC demonstrated the modified release curve with the mean rate of 71.18 ± 0.83% and 81.01 ± 0.74% at 15 min and 24 h, respectively, at pH 4.0. Conclusion: In conclusion, EMC suggested in this study was promising modified release formulation with high encapsulation efficiency and simple preparation method.