In this paper, we report a novel, efficient and versatile process to produce high concentrations of silver nanoprisms, while controlling their size (prism height) and size dispersity, using a "modified polyol process" (microwave-assisted process). If the formation of silver spherical particles, nanocubes or nanowires has already been reported using the classical polyol process (reduction of AgNO3 by ethylene glycol and in presence of PVP), here we show that the production of silver nanoprisms/nanoplates is possible by a careful choice in the process parameters and in particular in the reducing agent (ethylene glycol should be replaced by a reducing agent containing only one hydroxyl reducing group such as ethylene glycol monoalkyl ethers). The synthesis, characterization, the influence of parameters and the mechanism of formation are discussed in order to correlate the operational conditions with the shape and the dimension of the nanoparticles.