This study investigated the effects of harvesting at different plant maturation stages on the yield and component compositions of aniseed. It was carried out on the Harran Plain (Sanliurfa, Turkey) in the 2002 and 2003 growing seasons. A randomized complete block design was used. The plants were harvested at 10 different growth stages and determinations were made of the yields of seed, the essential oil and its main component (E)-anethole, the weight of 1000 seeds, the number of umbels per plant, the number of seedless umbels per plant and number of seeds per umbel. Statistical analyses indicated that all properties studied were affected by the harvesting stage. The fourth harvesting stage gave the highest yields of seed, essential oil and (E)-anethole. The first and second harvesting stages provided the best quality of essential oils with a high (E)-anethole content.