In order to evaluate the effect of planting patterns on radiation use efficiency and dry matter accumulation of sunflower an experiment was conducted as factorial layout based on a randomized complete block design with three replications at Mohaghegh Ardabili University during growing season of 2012-2013. Treatments included three levels of planting pattern (including 45×27.5, 60×20.5, 75×16.5 cm) and three sunflower cultivars (Armavirski, Azargol and Progress) with the density of 8 plant m-2. Results showed the effect of planting pattern significantly affected photosynthesis active radiation on the bottom of sunflower canopy at 58 days after sowing. Interaction of planting pattern and cultivar was significant on the middle of canopy at 57 and 71 days after sowing time. The highest radiation use efficiency belonged to Azargol at 84 and 114 days after sowing. While leaf area index of Azargol cultivar was less than the others. By considering that leaf area index had an inverse relationship with radiation use efficiency it seems that reduction of leaf area index caused to increase of radiation use efficiency in Azargol cultivar.
