The purpose of this study was to investigate the influence of roller compaction parameters on granule and tablet quality of a dry herbal extract from St. John's wort (Hypericum perforatum L.), which is widely used in the treatment of mild to moderate depressive disorders. Eight different extract batches were blended with 0.5, 2, and 5% of magnesium stearate and were compacted at different compaction forces using a gap width and force controlled roller compactor. The ribbon formed was milled into granules having mean particle sizes up to 700 microns. The roller compaction of the extracts decreased significantly the angle of repose from about 45 to 32 degrees and the Hausner ratio from about 1.2 to 1.1. Tabletting of granulated extract instead of extract powder effectively reduced not only dust and feeding problems during the tabletting process but also prevented capping. The incorporation of 2 and 5% of magnesium stearate into the roller compacted extract reduced significantly the sticking of the dry herbal extracts to the punch faces without affecting the crushing strength of the tablets. Tablets containing granulated extracts exhibited a 3-fold lower disintegration time of about 12 min compared to tablets containing extract powder. Dissolution studies revealed that hyperforin, hypericin, and rutin were more rapidly released from tablets containing granulated extract. Therefore, roller compaction leveled out the differences in technological properties between the eight dry herbal extracts and compression of granulated extract significantly improved tablet quality.