The cumin (Cuminum cyminum L.) is an annual plant of Apiaceae. It is generally used as a food additive for increasing the flavour of different food preparations. The fruits (often called seed )are rich in essential oil with the main constituents at different harvesting time being cumin aldehyde (19.9-23.6%), p-mentha-1,3-dien-7-al (11.4-17.5 %) and p-mentha-1,4-dien-7-al (13.9-16.9). The results of GC and GC/MS analysis showed that the fruits should be harvested at the ripe stage for ideal volatile oil yield and composition. The effect of different harvesting times on the yield and ratio of main components of the essential oil are evaluated.