A method of manufacturing a multi-core optical fiber, the method including assembling together a plurality of substantially identical polished single-core optical fiber preforms (2', 2"), referred to as "single-core preforms", each of which includes a core bar (3) surrounded by a layer of optical cladding (4), so as to form a "multi-core preform" (10), and drawing down the multi-core preform (10) so as to obtain the multi-core optical fiber. The assembly step includes securing the single-core preforms (2', 2") to one another by fusing them over their entire lengths or over portions thereof along their tangential lines of contact (T), without inserting the multi-core preform (10) into a holding tube. A vacuum is maintained in the preform during the drawing step, the vacuum being formed before or during the drawing step.