Characteristics of phytin storage in mature flax seeds, namely, concentration range, effect of weather and climatic conditions of the vegetation period, and morphology and size of phytate globoids in aleurone grains, have been determined. The content of phytic acid in flax seeds harvested in 2005–2009 ranged from 29.3 to 35.4 g/kg. High amounts of precipitation and low average daily temperature during seed ripening promoted accumulation of large amounts of phytin in seeds. Scanning electron microscopy showed that phytin globoids in the storage parenchyma of flax cotyledons are electron-dense spherical concretions ranging from 2.3 to 5.6 μm in diameter. Element composition analysis showed that phytic acid salts from flax contained K, Mg, Mn, Ca, and Fe.