A knowledge of physical properties of sunflower seed is essential for the design and development of such processing equipment as handling, separating, dehulling and storing. In this research, physical properties of sunflower seed, (Azargol variety as a case of study, was investigated at various moisture contents (3-14% d.b) and in three categories of big, average and small sizes samples. The results revealed that the seed length is strongly correlated with its width and thickness. Also, there was a significant connection observed between width and thickness of seed; however there was no significant connection observed between dimentions and its mass. The results showed that mass, thousand grain mass, porosity and terminal velocity of sunflower seed linearly increased with increase in its moisture content from 3% to 14% in each of the size categories. In all sizes categories, the bulk density of sunflower seeds linearly decreased with increase in moisture content from 3 to 14 %. In addition, the obtained results revealed that static coefficient of friction on some five studied surfaces increased linearly as moisture content increased from 3 to 14% for both cases of seed and kernel. The greatest value of static coefficient was found to occur on aluminum surface and for big size seeds, within the range of 0.42 to 0.45.