We have successfully prepared cell-sized giant liposomes encapsulating desired amounts of actoHMM, a mixture of actin filament (F-actin) and heavy meromyosin (HMM, an actin-related molecular motor), in the presence of 5 mM MgCl 2 and 50 mM KCl. We employed a spontaneous transfer method to prepare those liposomes. In the absence of HMM, F-actin was distributed homogeneously inside the liposomes. In contrast, when F-actin was encapsulated in liposomes together with HMM, network structures were generated. Such network structures are attributable to the cross-linking of F-actin by HMM.