Zanamivir is currently used for the treatment of H1N1 and H5N1 influenza viruses. Due to its highly hydrophilic property, zanamivir has poor oral bioavailability. Liposomal formulations are known to improve oral absorption of hydrophilic drugs. The present study investigates the effect of liposomes encapsulating zanamivir on the permeation of zanamivir across Caco-2 monolayers. Among the formulations studied, neutral liposomes composed of Phospholipon(®) 90 G and cholesterol at molar ratio of 7:3 gave the highest entrapment efficiency of zanamivir. The extrusion of liposomes loading zanamivir (LZV) resulted in the reduced-size liposomal zanamivir (RLZV), which had mean diameter at 283±42 nm and gave higher encapsulation efficiency of zanamivir at 34.69±6.37% compared to 28.32±5.25%. Transport studies across Caco-2 cell monolayers showed that the apparent permeation coefficients (P(app)) of LZV and RLZV were respectively 2.2- and 3.0-fold greater than that of zanamivir solution. The P(app) of RLZV was 1.4-fold higher than that of LZV. On the basis of these results, liposomes are able to improve permeability of zanamivir across the Caco-2 monolayers, thereby possibly enhancing oral bioavailability of zanamivir.