Weed chemical control has negative results on agroecosystems. Therefore, identification of cultivars tolerant to weeds has importance in nonchemical management. So, in this study, the tolerance of some alfalfa cultivars was studied to dodder. Anexperiment was conducted at research farm and laboratory of Shahed University in 2011. The farm experiment was done as split plot in time in randomized complete block design with three replicates. The treatments were included 12 alfalfa cultivars. The results showed that Local Hamedani and Fao were most sensitive and tolerant cultivars, respectively. Therefore, in laboratorial experiments, the effect of seed aqueous extract of Local Hamedani and Fao cultivars was evaluated on dodder seed germination. The experiment was conducted as factorial in randomized complete block design. The factors were seed extract of tolerant and susceptible cultivars of alfalfa at 5 levels, including zero (distilled water), 25, 50, 75 and 100 percent concentration. The results indicated that the effect of different concentrations of the extract was not significant on dodder seed germination, but the effect of cultivar and interaction of cultivar and concentration were significant on dodder seed germination. Dodder seed germination decreased as Fao seed extract concentration increased while a reverse trend was seen in Local Hamedani cultivar. In general, it seemed that Local Hamedani cultivar has some substances in seed that could stimulate dodder germination however there was not seen such a result in Fao, the tolerant variety. Complementary experiments are decisive to attain accurate results.