The present investigation was undertaken to fabricate porous nanoparticles of metoprolol tartrate by spray-drying using ammonium carbonate as pore former. Prepared nanoparticles were coated with Eudragit S100 polymer in order to prevent the release of metoprolol tartrate in the upper GI tract. It was shown that nanoparticles with low size ranges can be obtained with a low feed inlet rate. Micromeritic studies confirmed that nanoparticle batches are discrete and free flowing. Effects of the pore former on drug loading, porosity and