Rab GTPases and SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) are evolutionary conserved essential components of the eukaryotic intracellular transport system. Although pairing of cognate SNAREs is sufficient to fuse membranes in vitro, a complete reconstitution of the Rab-SN ARE machinery has never been achieved. Here we report the reconstitution of the early endosomal canine RabS GTPase, its key regulators and effectors together with SNAREs into proteoliposomes using a set of 17 recombinant human proteins. These vesicles behave like minimal 'synthetic' endosomes, fusing with purified early endosomes or with each other in vitro. Membrane fusion measured by content-mixing and morphological assays requires the cooperativity between RabS effectors and cognate SNAREs which, together, form a more efficient 'core machinery' than SNAREs alone. In reconstituting a fusion mechanism dependent on both a Rab GTPase and SNAREs, our work shows that the two machineries act coordinately to increase the specificity and efficiency of the membrane tethering and fusion process.