The effects of salicylic acid on grain growth of three wheat cultivars were studied underrainfed conditions. Factors were three cultivars of wheat (Sardari, Azar 2 and Son 60)and six levels of salicylic acid (untreated seed as control, zero or hydroprim, 500, 1000,1500 and 2000 µM). The results showed that, the effects of factors and their interactioneffects on grain filling rate and duration, grain yield, grain protein percent, 1000 grainweight and final weight of dry seed were significant. Seed priming with salicylic acidincreased grain growth in all cultivars compared to control and hydroprim treatments.Lag phase of grain growth curves, in all cultivars and priming treatments was short;maybe water stress lowered this period and decreased it. Among the cultivars, Sardarihad the highest grain growth rate, especially in the end of growth stage. Nearly 48 daysafter flowering, all cultivars got their constant weight. In all cultivars, priming especiallybetween 500-1500 µM showed the most rate and duration of grain filling. In general,application of salicylic acid improved grain yield, 1000 grain weight, rate and duration ofgrain filling compared to the control treatment in all cultivars under rainfed conditions.