Allelopathy is the biochemical interaction of inhibition and promotion that have significant roles in research involving sustainable agriculture. In order to evaluate the allelopathic effects of saffron (Crocus sativus L.) corm and petal aqueous concentrations on germination characteristics and preliminary growth of three weed species including redroot pigweed (Amaranthus retroflexus L.), whitetop (Cardaria draba L.) and flixweed (Descurainia sophia L.), an experiment was conducted based on a completely randomized design with four replications at Special Crop Laboratory, College of Agriculture, Ferdowsi University of Mashhad during 2010. Treatments included aqueous concentrations of saffron corm (C) and petal (P) at 25, 50 and 100%. Distilled water was used as control. Studied traits were final germination percentage (FGP), mean germination time (MGT), germination rate (GR), cumulative germination, radicle and plumule lengths, radicle to plumule length ratio and fresh weight of seedling for three weed species. Results showed that the corm and petal extracts had significant effects on FGP, GR, MGT, radicle and plumule lengths and seedling fresh weight of seedling for three weed species. P100 and C100 had the most potent inhibitory effect on FGP. By increasing in concentration enhanced MGT and decreased redicle length for three weed species. Also, inhibitory effect of aqueous extract on radicle growth was more than plumule. C25 had a stimulatory effect on plumule length of three weed species. C100 and P100 were reduced plumule length of weeds with 11.8-22.3 and 16.7-39.4 percent compared to control, respectively. Seedling fresh weight of whitetop and flixweed were increased in C25 compared to the control, but other treatments reduced weed seedling fresh weight.