In Algeria, drought affects grain weight and modified its biochemical composition. The present study was conducted to evaluate the effect of two water supplies (100% FC, 30% FC) on grain weight and composition of five genotypes of durum wheat (Triticum durum Desf.). We also examined the effects of shading of peduncle, spike and the entire plant and excision of awns, flag leaves and foliar system on grain weight, starch and amylose/amylopectin ratio. From this study, we found that grain weight was significantly reduced by the application of water deficit. However, this action is greatly related to genotype type. It is admitted that this trait is strongly conditioned by the grain filling process. The morphological characteristics of plants were implicated to grain weight elaboration. Among organs studied, the photosynthetic rate of spick and reserves remobilization from stem announced determinant in grain filling. We found also that starch content which is associated to amylose/amylopectin ratio is strongly related to grain weigh. Finally, grains weight variations were associated to starch content and mainly related to the water supply condition.