The aim of the present study was to investigate the effect of liposome-encapsulation and liposome-size on the in vivo pharmacokinetics of interferon ${alpha}$-2b ($IFN{alpha}$-2b) following i.m. administration to rats, and whether there was any liver-targeting of these liposomes. Since liposomes of different sizes can be obtained by homogenization, the effect of homogenization on the $IFN{alpha}$-2b activity was also investigated. The pharmacokinetics of $IFN{alpha}$-2b solution ($12.8{mu}g/kg$) and $IFN{alpha}$-2b prepared in liposomes, including three mean sizes of 172 nm ($12.2{mu}g/kg$), 113 nm (44.2, 11.0, and $2.8{mu}g/kg$, respectively), and 82 nm ($13.1{mu}g/kg$), were studied after a single i.m. dose to rats. Compared to a solution of $IFN{alpha}$-2b. administration of liposomal $IFN{alpha}$-2b resulted in a significantly prolonged $t_{max}$, the apparent elimination half life ($t_{1/2{eta}}$) was 2.3 times longer, both $AUC_{0-{infty}}$ and $MRT_{0-{infty}}$ were also clearly enhanced and greater accumulation was obtained in the liver (p < 0.05). The $AUC_{0-{infty}}$ increased proportionally to the administered dose of $IFN{alpha}$-2b liposomes. Moreover, the size of liposomes ranging from 82 nm to 172 nm had no significant difference on the pharmacokinetic behavior in vivo (p > 0.05). In sum, compared with the free form, $IFN{alpha}$-2b encapsulated in liposomes can alter strikingly the pharmacokinetics properties following i.m. injection and if a liposomal size ranging from 82 nm to 172 nm was used, consistent pharmacokinetic behaviors of $IFN{alpha}$-2b was exhibited. The liposomal formulation apparently targeted the liver, offering a potential advantage for hepatitis B treatment.