The aim of the research was to evaluate the influence of herbal raw materials granulation on changes in the content and composition of essential oil. The following ground materials and granulates were subjected to analysis: Thymi Herba (Thymus vulgaris L.), Salviae Herba (Salvia officinalis L.), Menthae Piperitae Herba (Mentha piperita L.) and Chamomillae Anthodium (Chamomilla recutita L.). Studies revealed that granulation of raw materials causes an increase in the final product density. i.e. for C. recutita it increased about 4.0-fold, for S. officinalis about 3.4-fold, for T. vulgaris about 2.6-fold, and for M. piperita about 1.6-fold. Moreover, granulation negatively affected the essential oil content in the evaluated raw materials, resulting in the following losses: about 56.6% for T. vulgaris, about 73.6% for S. officinalis, about 71.3% for M. piperita and about 43.9% for C. recutita. Furthermore, significant changes in the composition of essential oils isolated from granulates were observed with reference to ground materials, e.g. the percentage of iso-menthol in oil achieved from M. piperita granulate increased from about 29% to about 40%, that of camphor in oil from S. officinalis granulate was 14% in relation to about 8%, and that of thymol in oil from T. vulgaris granulate increased from about 44% to about 67%, whereas the percentage of a-bisabolol oxide A in oil from C. recutita granulate decreased from about 34% to about 18%. Copyright (C) 2008 John Wiley & Sons, Ltd.