The present invention is directed to a suspension of particles for delivering active principles, in particular proteins. Said particles are based on a diblock copolymer consisting of a neutral hydrophobic alpha hydroxy carboxylic acid polymer block and a hydrophilic linear polyaminoacid block with peptide alpha chaining, at least partly ionized. Said alpha hydroxy carboxylic acid polymer/linear polyaminoacid delivery particles spontaneously obtainable in the absence of surfactant can be stable. Said delivery particles are capable of being associated undissolved in colloidal suspension with at least an active principle and of delayed or prolonged release thereof. The invention is also directed to a powdery solid from which are derived the delivery particles and the preparation of said solid and said delivery particle suspension.