Abstract. Ultraweak luminescence (UWL) from mealy and vitreous wheat grain was investigated. Before the investigation the mealy and vitreous wheat grains were moistened in water for a period of 2,4,6 and 8 h. The grains were then dried to the mass they had before moistening. UWL measurements were made twice before and during imbibition of the grains. At the imbibition phase UWL was measured for 8 h. It was observed that UWL depended on the grain structure and the time of moistening. As moistened grain was of a more porous structure a higher UWL emission in the initial phase of imbibition was noted. Then UWL from the grains with a more porous structure quickly decayed. Finally after 8 h of imbibition UWL from moistened and not moistened grains was of similar intensity.