Allelopathy is a natural phenomenon and an important interaction among plant species. In this investigation, allelopathic effects of yarrow’s (Achillea millefolium) different organs aqueous extract were examined on germination and seedling growth of wheat (Triticum aestivum). This examination was conducted as completely randomized design with three replications in the University of Tabriz, Iran during summer 2017. All of the experiments were done in the lab condition and Petri dishes. The results indicated that the leaf, flower and whole plant extract caused a reduction in germination and growth of wheat seedlings. The highest reduction values in germination percentage and index, shoot, root and seedling length, shoot and root fresh weight and shoot and root dry weight were recorded at about 39, 43, 74, 78, 73, 66, 25, 56 and 33%, respectively. In contrast, the stem and root extract increased the mentioned parameters except germination percentage and germination index, about 11, 47, 26, 54, 220, 68 and 62%, respectively. The results showed that different organs of yarrow had dual allelopathic effects (both stimulatory and inhibitory effects) on wheat germination.