Essential oil composition of rosemary plays a decisive role on product quality. There are many parameters which can influence the herbal plants’ essential oil composition. It was aimed to determine the effect of location and harvesting time on essential oil composition of rosemary. The herbal materials evaluated within the scope of the study were harvested monthly from three different locations (Karaisalı in Adana, Tarsus in Mersin and Döşemealtı in Antalya) throughout the year in the Mediterranean Region, where rosemary production is common in Turkey. Essential oil composition of samples was analyzed by gas chromatography-mass spectrometry/flame ionisation dedector (GC-MS/FID) device equipped with capillary column. The main components of rosemary essential oil were determined as 1,8-cineol, camphor, α-pinene, borneol and α-terpineol. Essential oil composition of samples was influenced significantly by their location and harvesting time. The essential oil compositions in the samples obtained from Adana and Mersin were similar and the ratio of 1,8-cineol, which was the main component, varied between 52.56 and 58.26% and between 54.76 and 61.54%, respectively. On the other hand, main components were camphor (16.31-21.11%), 1,8-cineol (15.00-16.95%), α-pinene (14.38-17.88%), verbenone (10.94-13.57%) and borneol (9.04-12.19%) for Antalya location samples’ essential oil. There were also statistically important differences in the composition of rosemary essential oil according to harvesting time, but the range of this variation was narrow in comparison to locations. Results indicated that in essential oil production it should be taken into account that there might be differences in rosemary essential oil composition according to location and harvesting time.