Abstract: The invention relates to vectors for delivering medicinal, nutritional, plant-protection or cosmetic active principles, these delivery particles being of small, controllable and adjustable particle size, which protect the active principle, and being biocompatible, biodegradable, non-immunogenic, stable and free of solvent. The particles do not denature the active principle and allow the active principle to be released. The microparticles of the invention are of a cohesive structure made of a physicochemically stable and integral composite gel which includes an oil such as coconut oil, an aqueous phase and a linear, non-crosslinked copolyamino acid of Leu/Glu type (random or diblock). The microparticles have a controllable and adjustable size of between 0.05 and 500 &mgr;m.