In order to investigate the allelopathic effects of Papaver chelidoniifolium, Chelidonium majus and Roemeria refracta (Papaveraceae), an experiment was conducted based on complete randomized design with 4 replications in physiology laboratory of Azad University of Gorgan in 2010. After breaking seed dormancy by GA3 (1000ppm-24h) treatments 0%, 25%, 50%, 75%, 100% of plants water extracts were applied. Results showed that water extracts in three genus of Papaveraceae in 100% concentration caused reduction in Ph. paradoxa germination, significantly. Water extracts effect on root and shoot length, dry weigh of root and shoot were significant (p<0.05). The most reduction effect on seed germination and growth factors in three genuses, belong to Ch. majus in several concentration.