The research was carried out with the aim to determine the drug yield, essential oil rate and changes in the composition of volatile oil of hyssop in growth stages on the harvest date, different times on the day and plant organs. Samples were taken in the year of 2010, at Field Crops Experimental Area of Agriculture Faculty of Suleyman Demirel University at four different growing stages (budding, first blooming, full blooming and last blooming) and at three different times on the day (morning-08 : 00, mid-day-13 : 00 and evening-18 : 00). At each collecting time, 10 plant samples were used for analysis. Essential oil components were identified by GC/MS. In the research, the highest fresh herb, drug herb, flower and stem yield (7402, 3025, 750 and 1606 kg/ha, respectively) were observed from last blooming stage. The highest leaf yield (1224 kg/ha) was determined from first blooming stage. The highest essential oil ratio (0.57%) was determined from flowers at full blooming stage. The highest essential oil yield (9.2 kg/ha) was obtained from herb at full blooming stage. The highest essential oil ratio was determined at evening hours in both fresh herb and dry herb (0.14 and 0.48%, respectively). The main compounds of hyssop essential oil were determined as sabinene (28.4-57.2%), heneicosene (9.49-37.0%), geranyl acetate (7.5-25.0%), myrcene (2.5-10.5%), farnesene (1.3-7.5%) and camphor (0.8-8.1%).