The aim of the research was to test the effect of Al dose and Al form on carbohydrates content and composition and on changes in photosyntesis efficiency of two lettuce cultivars. The research was carried out in a vegetation hall using vases (2 dm3 capacity) filled with clean quartz sand. The plants were fed on full mineral nutritients which contained mmol: Ca(NO3)2 – 3.74; (NH4)2SO4 – 2.14; (NH4)2HPO4 – 1.61; KCl – 6.36; MgSO4 – 2.09. Apart from the ingredients mentioned above each vase was administered 2 cm3 A-Z solution and 1% C6H5FeO7 H2O solution. Furthermore Al in the amount 0,5 and 20 mg dm-3 in mononuclear or polynuclear form was inserted to the ground. During the vegetation period plants’ photosyntesis activity was measured. After the harvest carbohydrates content in the dry mass was analysed. The results showed that along with an increase of Al amount in the ground, especially in the polynuclear form, carbohydrates content decreased. It caused that the level of photosyntesis efficiency of two lettuce cultivars decreased. But the decrease tendency was more clearly observed in ‘Justyna’ cv. in comparison to ‘Beata’ cv.