Bortezomib is the first therapeutic agent designed to inhibit mainly the activity of the 26S proteasome. It is used for the treatment of multiple myeloma. The objective of this study was to develop and optimize liposomal formulation of bortezomib in order to improve the encapsulation efficiency. For evaluating the encapsulation efficiency it was investigated the effect of two parameters: the drug/lipid molar ratio and the pH of the medium. The liposomal formulation of bortezomib was obtained by mixing a solution of bortezomib with SUV liposomes (small unilamellar vesicle). A transmembrane pH gradient was obtained by creating a difference of pH between internal medium of the liposomes and the external medium in which the liposomes were suspended. When preparing the liposomes by using a pH gradient it was obtained an encapsulation efficiency of 48 % for the molar ratio bortezomib:lipid 1:5.