In order to evaluate effect of Azotobacter chroococcum strains on yield, yield components and qualitative indices of winter rapeseed (Brassica napus L.), an experiment was conducted during 2009-2010 growing season at Research Institute of Rice in Rasht. The experimental design was completely randomized block, with three replications. Investigated treatments were including control (without seed inoculation), seed inoculation with Azotobacter chroococcum strains 6, 9, 11, 12, 13, 14, 15, 16, 19, 21, 23, 25, 28, 35 and 38. Results showed that Azotobacter chroococcum significantly affected on all traits. The highest of seed oil yield and K, P, Mg content caused by A. chroococcum strain 14. A. chroococcum strain 12 caused the highest of seed yield with average of 3532.43 kg/ha that hadn’t significant difference with strains 9 and 14. As A. chroococcum strain 12 caused the highest of seed yield components and N, Ca, oil seed content. Growth promoting hormones production, N2 fixation, mineral nutrients dissolubility such as phosphorus, siderophore production and kinds of antibiotics are the effect of Azotobacter chroococcum mechanisms that seems to be using at least one of these mechanisms is increased plant yield. Generally, A. chroococcum strain 12, A. chroococcum strain 14 and A. chroococcum strain 9 had more positive effect on traits compared with other strains. Results of this experiment showed the use of A. chroococcum increases yield and qualitative characteristics of rapeseed and therefore can be used as supplementary of chemical fertilizers.