In order to evaluate the effect of priming and seed size on yield, yield components and some storage characteristics of onion genotypes this research was conducted at the Agriculture and Natural Resources Research Center of East Azarbayjan, Iran in two cropping seasons 2012 and 2013. The factorial was conducted based randomized complete block design (RCBD) with three replications.The experimental treatments included priming (at four levels: hydro priming, osmopriming (in %2 KNO3), priming with falommin substance (in 2%) and control (without priming), seed size (at three levels: small, medium, large) and genotypes (at two levels: Red Azarshahr and Zargan). Following characteristics such as total yield (TY) , mean bulb weight (BW), bulb diameter (BD), bulb length (BL), number of leaves, plant high (PLH) , number of bulb skin and center on the basal plate, number and scale diameter, bulb diameter at the  neck and base were studied. Analysis of variance for the measurd traits indicated that all studied characters were significant in 1% level of probability. Seed size × priming interactions effects were significant for TY, BW, PLH and number scale but the significant differences were not observed in the other traits. The results indicated that primed was improved  the yield and yield components. In a way mean comparsions of the pre-teratment showed that the highest total yield was obtained from plant that primed with folammin amino acid and the lowest was achieved from control plants (59.37 t ha^-1 and 38.41 t ha^-1 respectively). Also mean comparison indicated that the higher total yield (58.80 t ha^-1) was obtained from large seed size and the lower (37.89 t ha^-1) of it was found to small seed size.Therefore, primed with folamin amino acid and large seed are recommended of onion planting for the places with the same environmental conditions of this experiment