The aim of the research was determining the allelopathic effect of juniper essential oil (EO) on germination and seedling growth in lettuce. The experiment was conducted as a randomized complete design with four replicates. Five levels of essential oil (100, 200, 500, 1000 & 2000 ppm) were applied and distilled water as control treatment. The measured parameters were germination percentage (GP) and germination rate (GR), cumulative percentage, seedling length, fresh and dry weight. The result showed that GP in levels of 1000 & 2000 ppm significantly decreased and in other levels not significant differences was detected in comparison to control. GR in seeds treated with 100 & 200 ppm had not significant differences but in higher levels GR significantly decreased. Maximum length of shoot and root were observed in control (2/63 & 5/42 cm, respectively) and different levels of EO significantly decreased the seedling length in comparison to control. The fresh weight of shoot and root were significantly decreased with increasing in concentrations of EO, but the differenced was not significant in concentrations near to each other. With increasing level dry weight of shoot and root were significantly decreased, except in 100 ppm. In general it can be conclude that juniper essential oil had significant allelopathic effect on germination parameters of lettuce.

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