Abstract The chemical variation of volatile constituents from leaves of Pimenta pseudocaryophyllus collected bimonthly for one year from a locality in the Atlantic Rain Forest, southeastern Brazil, was determined by GC/MS. Seven com- pounds were identified and characterized, revealing a predominance of phenylpropanoids (15.4â70.9%) and variable amounts of monoterpenes (0.5â5.3%). The composition of the oil changed month by month. The best yield of oil was obtained in November, and the major component chavibetol was present in all samples (50.2â70.9%). The chavibetol content showed significant seasonal variation, with the maximum percentages of 69.1% and 70.9% measured in January and November, respectively Key Word Index: Seasonal variation Pimenta pseudocaryophyllus chavibetolessential oil